Wood moisture meter

I bought one of those cheap wood moisture meters on sale for $25 at Princess Auto some time ago. I never actually tried it out until I cut up some fresh lumber on my bandsaw and wanted to get some measure of how fast it dried.

Unfortunately, the moisture meter didn't last very long. Knowing that probe penetration into the wood makes a big difference in terms of how well they make contact, I kept tapping the meter in with my wrist. It took some very firm taps to get even minimal penetration into the hardwood, but after just a few readings, it stopped working.

When I popped it open, I saw that the probe points were soldered directly into the circuit boards. One of the pads had come off the circuit boards and the trace to the next circuit component (right where the pencil tip points to) was broken.

With such flimsy construction, there wasn't much sense trying to repair the damage. It would just break again next time I'd use it.

So I set out to make a new set of external probes for the meter. These would be probes that I could drive in with a hammer.

I started with some long narrow screws and ground them to a point. Then I smoothed them to a shine with a buffing wheel. I figured getting the sides of the probes smooth would make it easier to pull them back out of the wood.

I mounted the probes in some layers of white plastic that I had cut from a bucket. A block of UHMW plastic would have been better, but I didn't have any of that stuff handy.

Normally, I would have been tempted to just use a block of wood to mount the probes in, but moisture meters work by measuring conductivity of the wood. If I mounted the probes in wood, that would completely mess up my readings.

I put a nut over the points of my probes, then added three more layers of plastic over the points to serve as a limit for how far the tips could be pushed into the wood. I also attached a wooden knob as a handle.

I took the original probes out of the meter and just soldered some wires to where the probes used to be.

The probe unit can be driven into the wood with a mallet to ensure that it penetrates to full depth, even in hardwood.

The piece of wood I'm checking here is still relatively fresh from having been sliced off a log, so it's still saturated with moisture.

Using a multimeter to measure wood moisture

Next I researched how moisture meters actually work on the web. I found that all they do is measure DC electrical resistance of the wood, and use that to calculate moisture content. So I figured, why not just use a multimeter to measure the resistance and calculate the moisture content myself?

The catch with this is that a typical multimeter will read up to about 20 megohms in resistance mode, and the resistance between the two probes for any "normal" moisture content is often in the hundreds of megohms. So the multimeter wouldn't be able to measure it.

But there is a trick to measuring much higher resistance with a cheap multimeter.

Most of these multimeters, when in voltage measurement mode, have an internal resistance of about 10 megohms. That is to say, the meter itself is like a 10 megohm resistor that just happens to display the voltage across it. I checked, using another multimeter, that this meter was one of those with the 10 megohm resistance.

So now if I use a 9-volt battery, and hook the volt meter and my wood probes in series with each other, the voltage drop across my meter and the wood will be equal to the 9 volts from the battery. And the voltage drops across the meter and the probes will be in the same proportion as their resistances.

Knowing that current is equal to voltage divided by resistance, and that the current through each element is the same, we can express this as:

Current = V_bat = V_meter = V_wood

R_meter + R_wood R_meter R_wood

For example, if the wood between the probes has an 80 megohm resistance, my meter has a 10 megohms resistance, and my battery is 9 volts, I should see an 8 volt drop across the wood and a 1 volt drop across the meter. So if my meter reads 1 volt, I know that the resistance is 80 megohms.

V_bat = V_meter + V_wood Now, through a bunch of algebraic manipulation, we can solve for R_wood as a function of known variables V_bat, V_meter and R_meter:

R_wood = R_meter ( V_bat - 1 )

V_meter

By taping and connecting a nine volt battery to one of the probes, we can now measure the voltage across the meter with the probes (two nails in the wood) in series with the meter.

With the meter indicating 3.33 volts, we can solve for a resistance of 17 megohms.

Now we can use the following resistance data to convert that to wood moisture content.

This graph was generated from the data below.

The average electrical resistance along the grain of several species of wood at different levels of moisture content¹
Source:http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr06.pdf

Wood species Moisture content
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Conifers
Baldcypress 12,600 3,980 1,410 630 265 120 60 33 18.6 11.2 7.1 4.6 3.09 1.78 1.26 0.91 0.66 0.51 0.42
Douglas-fir (coast region) 22,400 4,780 1,660 630 265 120 60 33 18.6 11.2 7.1 4.6 3.09 2.14 1.51 1.1 0.79 0.6 0.46
Fir, California red 31,600 6,760 2,000 725 315 150 83 48 28.8 18.2 11.8 7.6 5.01 3.31 2.29 1.58 1.15 0.83 0.63
Fir, white 57,600 15,850 3,980 1,120 415 180 83 46 26.9 16.6 11 6.6 4.47 3.02 2.14 1.55 1.12 0.86 0.62
Hemlock, eastern 120,000 20,000 4,300 1,300 450 200 100 45 25 14 8.8 5.4 3.5 2.3 1.6 1.1 0.78 0.57
Hemlock, western 22,900 5,620 2,040 850 400 185 98 51 28.2 16.2 10 6 3.89 2.52 1.58 1.05 0.72 0.51 0.37
Larch, western 39,800 11,200 3,980 1,445 560 250 120 63 33.9 19.9 12.3 7.6 5.02 3.39 2.29 1.62 1.2 0.87 0.66
Pine, jack 450,000 52,000 9,500 2,800 1,000 440 210 110 60 35 21 13 8.8 5.8 3.8 2.6 1.8 1.3 0.98
Pine, longleaf 25,000 8,700 3,160 1,320 575 270 135 74 41.7 24 14.4 8.9 5.76 3.72 2.46 1.66 1.15 0.79 0.6
Pine, red 700,000 100,000 17,000 4,300 1,300 470 210 100 52 28 16 10 6.8 4.4 2.8 1.9 1.2 0.91 0.67
Pine, white 20,900 5,620 2,090 850 405 200 102 58 33.1 19.9 12.3 7.9 5.01 3.31 2.19 1.51 1.05 0.74 0.52
Pine, ponderosa 39,800 8,910 3,310 1,410 645 300 150 81 44.7 25.1 14.8 9.1 5.62 3.55 2.34 1.62 1.15 0.87 0.69
Pine, shortleaf 43,600 11,750 3,720 1,350 560 255 130 69 38.9 22.4 13.8 8.7 5.76 3.8 2.63 1.82 1.29 0.93 0.66
Pine, sugar 22,900 5,250 1,660 645 280 140 76 44 25.7 15.9 10 6.6 4.36 3.02 2.09 1.48 1.05 0.75 0.56
Redwood 22,400 4,680 1,550 615 250 100 45 22 12.6 7.2 4.7 3.2 2.29 1.74 1.32 1.05 0.85 0.71 0.6
Spruce, black 700,000 90,000 16,000 4,300 1,400 580 250 120 68 38 23 14 9.6 6.3 4.3 3 2.1 1.4 1
Spruce, Sitka 22,400 5,890 2,140 830 365 165 83 44 25.1 15.5 9.8 6.3 4.27 3.02 2.14 1.58 1.17 0.91 0.71

Hardwoods
Ash, black 14,000 2,300 600 200 85 40 20 10 6 3.4 2.1 1.3 0.9 0.6 0.42 0.32 0.25 0.2 0.17
Ash, white₂ 12,000 2,190 690 250 105 55 28 14 8.3 5 3.2 2 1.32 0.89 0.63 0.5 0.44 0.4 0.4
Aspen, bigtooth 300,000 24,000 4,000 1,100 360 150 60 30 16 8.6 5 3.1 2 1.3 0.88 0.61 0.43 0.33 0.26
Basswood₂ 36,300 1,740 470 180 85 45 27 16 9.6 6.2 4.1 2.8 1.86 1.32 0.93 0.69 0.51 0.39 0.31
Birch₂ 87,000 19,950 4,470 1,290 470 200 96 53 30.2 18.2 11.5 7.6 5.13 3.55 2.51 1.78 1.32 0.95 0.7
Birch, paper 200,000 24,000 5,000 1,400 550 230 110 57 30 17 10 6 4 2.5 1.7 1.1 0.81 0.59 0.43
Elm, American 18,200 2,000 350 110 45 20 12 7 3.9 2.3 1.5 1 0.66 0.48 0.42 0.4 0.4 0.4 0.4
Hickory₂ 31,600 2,190 340 115 50 21 11 6.3 3.7 2.3 1.5 1 0.71 0.52 0.44 0.4 0.4 0.4
Magnolia 43,700 12,600 5,010 2,040 910 435 205 105 56.2 29.5 16.2 9.1 5.25 3.09 1.86 1.17 0.74 0.5 0.32
Maple, sugar 72,400 13,800 3,160 690 250 105 53 29 16.6 10.2 6.8 4.5 3.16 2.24 1.62 1.23 0.98 0.75 0.6
Oak, northern red₄ 14,400 4,790 1,590 630 265 125 63 32 18.2 11.3 7.3 4.6 3.02 2.09 1.45 0.95 0.8 0.63 0.5
Oak, white 17,400 3,550 1,100 415 170 80 42 22 12.6 7.2 4.3 2.7 1.7 1.15 0.79 0.6 0.49 0.44 0.41
Walnut, black 51,300 9,770 2,630 890 355 155 78 41 22.4 12.9 7.3 4.9 3.16 2.14 1.48 1.02 0.72 0.51 0.38

Exotic hardwoods
Philippine mahogany 2,890 690 220 80 35 15 9 5 2.8 1.7 1.1 0.7 0.45 0.3 0.21 0.16 0.12 0.09 0.07
Sweetgum 38,000 6,460 2,090 815 345 160 81 45 25.7 15.1 9.3 6 3.98 2.63 1.78 1.26 0.87 0.63 0.46
Tupelo, black₄ 31,700 12,600 5,020 1,820 725 275 120 58 27.6 13 6.9 3.7 2.19 1.38 0.95 0.63 0.46 0.33 0.25
Yellow-poplar 24,000 8,320 3,170 1,260 525 250 140 76 43.7 25.2 14.5 8.7 5.76 3.81 2.64 1.91 1.39 1.1 0.85
Khaya₃ 44,600 16,200 6,310 2,750 1,260 630 340 180 105 60.2 35.5 21.9 14.1 9.33 6.16 4.17 2.82 1.99 1.44
Mahogany (Swietenia) 20,900 6,760 2,290 870 380 180 85 43 22.4 12.3 7.2 4.4 2.69 1.66 1.07 0.72 0.49 0.35 0.26

Wood species	Moisture content
	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25
Conifers
Baldcypress	12,600	3,980	1,410	630	265	120	60	33	18.6	11.2	7.1	4.6	3.09	1.78	1.26	0.91	0.66	0.51	0.42
Douglas-fir (coast region)	22,400	4,780	1,660	630	265	120	60	33	18.6	11.2	7.1	4.6	3.09	2.14	1.51	1.1	0.79	0.6	0.46
Fir, California red	31,600	6,760	2,000	725	315	150	83	48	28.8	18.2	11.8	7.6	5.01	3.31	2.29	1.58	1.15	0.83	0.63
Fir, white	57,600	15,850	3,980	1,120	415	180	83	46	26.9	16.6	11	6.6	4.47	3.02	2.14	1.55	1.12	0.86	0.62
Hemlock, eastern		120,000	20,000	4,300	1,300	450	200	100	45	25	14	8.8	5.4	3.5	2.3	1.6	1.1	0.78	0.57
Hemlock, western	22,900	5,620	2,040	850	400	185	98	51	28.2	16.2	10	6	3.89	2.52	1.58	1.05	0.72	0.51	0.37
Larch, western	39,800	11,200	3,980	1,445	560	250	120	63	33.9	19.9	12.3	7.6	5.02	3.39	2.29	1.62	1.2	0.87	0.66
Pine, jack	450,000	52,000	9,500	2,800	1,000	440	210	110	60	35	21	13	8.8	5.8	3.8	2.6	1.8	1.3	0.98
Pine, longleaf	25,000	8,700	3,160	1,320	575	270	135	74	41.7	24	14.4	8.9	5.76	3.72	2.46	1.66	1.15	0.79	0.6
Pine, red	700,000	100,000	17,000	4,300	1,300	470	210	100	52	28	16	10	6.8	4.4	2.8	1.9	1.2	0.91	0.67
Pine, white	20,900	5,620	2,090	850	405	200	102	58	33.1	19.9	12.3	7.9	5.01	3.31	2.19	1.51	1.05	0.74	0.52
Pine, ponderosa	39,800	8,910	3,310	1,410	645	300	150	81	44.7	25.1	14.8	9.1	5.62	3.55	2.34	1.62	1.15	0.87	0.69
Pine, shortleaf	43,600	11,750	3,720	1,350	560	255	130	69	38.9	22.4	13.8	8.7	5.76	3.8	2.63	1.82	1.29	0.93	0.66
Pine, sugar	22,900	5,250	1,660	645	280	140	76	44	25.7	15.9	10	6.6	4.36	3.02	2.09	1.48	1.05	0.75	0.56
Redwood	22,400	4,680	1,550	615	250	100	45	22	12.6	7.2	4.7	3.2	2.29	1.74	1.32	1.05	0.85	0.71	0.6
Spruce, black	700,000	90,000	16,000	4,300	1,400	580	250	120	68	38	23	14	9.6	6.3	4.3	3	2.1	1.4	1
Spruce, Sitka	22,400	5,890	2,140	830	365	165	83	44	25.1	15.5	9.8	6.3	4.27	3.02	2.14	1.58	1.17	0.91	0.71
Hardwoods
Ash, black	14,000	2,300	600	200	85	40	20	10	6	3.4	2.1	1.3	0.9	0.6	0.42	0.32	0.25	0.2	0.17
Ash, white₂	12,000	2,190	690	250	105	55	28	14	8.3	5	3.2	2	1.32	0.89	0.63	0.5	0.44	0.4	0.4
Aspen, bigtooth	300,000	24,000	4,000	1,100	360	150	60	30	16	8.6	5	3.1	2	1.3	0.88	0.61	0.43	0.33	0.26
Basswood₂	36,300	1,740	470	180	85	45	27	16	9.6	6.2	4.1	2.8	1.86	1.32	0.93	0.69	0.51	0.39	0.31
Birch₂	87,000	19,950	4,470	1,290	470	200	96	53	30.2	18.2	11.5	7.6	5.13	3.55	2.51	1.78	1.32	0.95	0.7
Birch, paper	200,000	24,000	5,000	1,400	550	230	110	57	30	17	10	6	4	2.5	1.7	1.1	0.81	0.59	0.43
Elm, American	18,200	2,000	350	110	45	20	12	7	3.9	2.3	1.5	1	0.66	0.48	0.42	0.4	0.4	0.4	0.4
Hickory₂		31,600	2,190	340	115	50	21	11	6.3	3.7	2.3	1.5	1	0.71	0.52	0.44	0.4	0.4	0.4
Magnolia	43,700	12,600	5,010	2,040	910	435	205	105	56.2	29.5	16.2	9.1	5.25	3.09	1.86	1.17	0.74	0.5	0.32
Maple, sugar	72,400	13,800	3,160	690	250	105	53	29	16.6	10.2	6.8	4.5	3.16	2.24	1.62	1.23	0.98	0.75	0.6
Oak, northern red₄	14,400	4,790	1,590	630	265	125	63	32	18.2	11.3	7.3	4.6	3.02	2.09	1.45	0.95	0.8	0.63	0.5
Oak, white	17,400	3,550	1,100	415	170	80	42	22	12.6	7.2	4.3	2.7	1.7	1.15	0.79	0.6	0.49	0.44	0.41
Walnut, black	51,300	9,770	2,630	890	355	155	78	41	22.4	12.9	7.3	4.9	3.16	2.14	1.48	1.02	0.72	0.51	0.38
Exotic hardwoods
Philippine mahogany	2,890	690	220	80	35	15	9	5	2.8	1.7	1.1	0.7	0.45	0.3	0.21	0.16	0.12	0.09	0.07
Sweetgum	38,000	6,460	2,090	815	345	160	81	45	25.7	15.1	9.3	6	3.98	2.63	1.78	1.26	0.87	0.63	0.46
Tupelo, black₄	31,700	12,600	5,020	1,820	725	275	120	58	27.6	13	6.9	3.7	2.19	1.38	0.95	0.63	0.46	0.33	0.25
Yellow-poplar	24,000	8,320	3,170	1,260	525	250	140	76	43.7	25.2	14.5	8.7	5.76	3.81	2.64	1.91	1.39	1.1	0.85
Khaya₃	44,600	16,200	6,310	2,750	1,260	630	340	180	105	60.2	35.5	21.9	14.1	9.33	6.16	4.17	2.82	1.99	1.44
Mahogany (Swietenia)	20,900	6,760	2,290	870	380	180	85	43	22.4	12.3	7.2	4.4	2.69	1.66	1.07	0.72	0.49	0.35	0.26

¹ Resistance measured in megohms at 80°F (27 °C) between two pairs of needle electrodes spaced 1-1/4 inches apart and driven to a depth of 5/16 inch. The reciprocals of these data are conductance in micro siemens.
² Exact species unknown.
³Known in the trade as "African mahogany."
⁴The values for this species were calculated from measurements on veneer.

You can also Download the Excel spreadsheet of this data

Unfortunately, the source data only indicates the depth of penetration, but not the actual diameter of the probes used to make the measurements. Much of the resistance is actually from the region nearest to the probes, as the cross sectional area that the electricity can flow across is only as large as the surface of the probes. For the distance between the probes, the current can spread over a much larger area. So the shape of the probes is actually more critical than the distance between probes.

I figured a reasonable probe diameter would be a small nail. I'm using nails with 1.85 mm (.073") diameter. The next challenge is to drive the nails the same distance into the wood as was done for the source data above. I needed a penetration of 5/16" or 8 mm.

The easiest way to get the depth and spacing consistent was to make a block of wood that was 8 mm shorter than the nails, with two holes that the nails loosely fit into.

The idea is to use the block as depth stop when driving the nails into the wood. The block of wood is then removed to take a resistance reading between the two nails.

An interesting property of wood is that for moisture content below 20%, resistance goes up almost exponentially with decreasing moisture content. Getting the resistance reading wrong by a factor of two will only throw the calculated moisture content off by about a percent. So getting the probe size and penetration depth exactly right is not that important. I did some experiments though and the resistance between the probes drops inversely with penetration depth. So if you want to get a deeper moisture reading, drive the nails 16 mm into the wood, then double your resistance reading to compensate for the deeper penetration before looking it up on the above table.

The approach can also be simplified by pre-calculating the whole table in terms of voltage readings on the multimeter. I recalculated the table for readings below 20% moisture content, so now all you have to do is look up the voltage on the table below to get the moisture content.

Voltage reading for cheap 10-megohm impedance meter in series with wood probes
This is for two probes about 1.8 mm in diameter, 32 millimeters apart, with 8 mm penetration.

Wood species Moisture content
7 8 9 10 11 12 13 14 15 16 17 18 19
Conifers
Baldcypress 0.007 0.023 0.063 0.141 0.327 0.692 1.286 2.093 3.147 4.245 5.263 6.164 6.875
Douglas-fir (coast region) 0.004 0.019 0.054 0.141 0.327 0.692 1.286 2.093 3.147 4.245 5.263 6.164 6.875
Fir, California red 0.003 0.013 0.045 0.122 0.277 0.563 0.968 1.552 2.320 3.191 4.128 5.114 5.996
Fir, white 0.002 0.006 0.023 0.080 0.212 0.474 0.968 1.607 2.439 3.383 4.286 5.422 6.220
Hemlock, eastern 0.001 0.004 0.021 0.069 0.196 0.429 0.818 1.636 2.571 3.750 4.787 5.844
Hemlock, western 0.004 0.016 0.044 0.105 0.220 0.462 0.833 1.475 2.356 3.435 4.500 5.625 6.479
Larch, western 0.002 0.008 0.023 0.062 0.158 0.346 0.692 1.233 2.050 3.010 4.036 5.114 5.992
Pine, jack 0.000 0.002 0.009 0.032 0.089 0.200 0.409 0.750 1.286 2.000 2.903 3.913 4.787
Pine, longleaf 0.004 0.010 0.028 0.068 0.154 0.321 0.621 1.071 1.741 2.647 3.689 4.762 5.711
Pine, red 0.000 0.001 0.005 0.021 0.069 0.188 0.409 0.818 1.452 2.368 3.462 4.500 5.357
Pine, white 0.004 0.016 0.043 0.105 0.217 0.429 0.804 1.324 2.088 3.010 4.036 5.028 5.996
Pine, ponderosa 0.002 0.010 0.027 0.063 0.137 0.290 0.563 0.989 1.645 2.564 3.629 4.712 5.762
Pine, shortleaf 0.002 0.008 0.024 0.066 0.158 0.340 0.643 1.139 1.840 2.778 3.782 4.813 5.711
Pine, sugar 0.004 0.017 0.054 0.137 0.310 0.600 1.047 1.667 2.521 3.475 4.500 5.422 6.267
Redwood 0.004 0.019 0.058 0.144 0.346 0.818 1.636 2.813 3.982 5.233 6.122 6.818 7.323
Spruce, black 0.000 0.001 0.006 0.021 0.064 0.153 0.346 0.692 1.154 1.875 2.727 3.750 4.592
Spruce, Sitka 0.004 0.015 0.042 0.107 0.240 0.514 0.968 1.667 2.564 3.529 4.545 5.521 6.307

Hardwoods
Ash, black 0.006 0.039 0.148 0.429 0.947 1.800 3.000 4.500 5.625 6.716 7.438 7.965 8.257
Ash, white2 0.007 0.041 0.129 0.346 0.783 1.385 2.368 3.750 4.918 6.000 6.818 7.500 7.951
Aspen, bigtooth 0.000 0.004 0.022 0.081 0.243 0.563 1.286 2.250 3.462 4.839 6.000 6.870 7.500
Basswood2 0.002 0.051 0.188 0.474 0.947 1.636 2.432 3.462 4.592 5.556 6.383 7.031 7.589
Birch2 0.001 0.005 0.020 0.069 0.188 0.429 0.849 1.429 2.239 3.191 4.186 5.114 5.948
Birch, paper 0.000 0.004 0.018 0.064 0.161 0.375 0.750 1.343 2.250 3.333 4.500 5.625 6.429
Elm, American 0.005 0.045 0.250 0.750 1.636 3.000 4.091 5.294 6.475 7.317 7.826 8.182 8.443
Hickory2 0.003 0.041 0.257 0.720 1.500 2.903 4.286 5.521 6.569 7.317 7.826 8.182
Magnolia 0.002 0.007 0.018 0.044 0.098 0.202 0.419 0.783 1.360 2.278 3.435 4.712 5.902
Maple, sugar 0.001 0.007 0.028 0.129 0.346 0.783 1.429 2.308 3.383 4.455 5.357 6.207 6.839
Oak, northern red4 0.006 0.019 0.056 0.141 0.327 0.667 1.233 2.143 3.191 4.225 5.202 6.164 6.912
Oak, white 0.005 0.025 0.081 0.212 0.500 1.000 1.731 2.813 3.982 5.233 6.294 7.087 7.692
Walnut, black 0.002 0.009 0.034 0.100 0.247 0.545 1.023 1.765 2.778 3.930 5.202 6.040 6.839

Exotic hardwoods
Philippine mahogany 0.031 0.129 0.391 1.000 2.000 3.600 4.737 6.000 7.031 7.692 8.108 8.411 8.612
Sweetgum 0.002 0.014 0.043 0.109 0.254 0.529 0.989 1.636 2.521 3.586 4.663 5.625 6.438
Tupelo, black4 0.003 0.007 0.018 0.049 0.122 0.316 0.692 1.324 2.394 3.913 5.325 6.569 7.383
Yellow-poplar 0.004 0.011 0.028 0.071 0.168 0.346 0.600 1.047 1.676 2.557 3.673 4.813 5.711
Khaya 0.002 0.006 0.014 0.033 0.071 0.141 0.257 0.474 0.783 1.282 1.978 2.821 3.734
Mahogany (Swietenia) 0.004 0.013 0.039 0.102 0.231 0.474 0.947 1.698 2.778 4.036 5.233 6.250 7.092

Wood species	Moisture content
	7	8	9	10	11	12	13	14	15	16	17	18	19
Conifers
Baldcypress	0.007	0.023	0.063	0.141	0.327	0.692	1.286	2.093	3.147	4.245	5.263	6.164	6.875
Douglas-fir (coast region)	0.004	0.019	0.054	0.141	0.327	0.692	1.286	2.093	3.147	4.245	5.263	6.164	6.875
Fir, California red	0.003	0.013	0.045	0.122	0.277	0.563	0.968	1.552	2.320	3.191	4.128	5.114	5.996
Fir, white	0.002	0.006	0.023	0.080	0.212	0.474	0.968	1.607	2.439	3.383	4.286	5.422	6.220
Hemlock, eastern		0.001	0.004	0.021	0.069	0.196	0.429	0.818	1.636	2.571	3.750	4.787	5.844
Hemlock, western	0.004	0.016	0.044	0.105	0.220	0.462	0.833	1.475	2.356	3.435	4.500	5.625	6.479
Larch, western	0.002	0.008	0.023	0.062	0.158	0.346	0.692	1.233	2.050	3.010	4.036	5.114	5.992
Pine, jack	0.000	0.002	0.009	0.032	0.089	0.200	0.409	0.750	1.286	2.000	2.903	3.913	4.787
Pine, longleaf	0.004	0.010	0.028	0.068	0.154	0.321	0.621	1.071	1.741	2.647	3.689	4.762	5.711
Pine, red	0.000	0.001	0.005	0.021	0.069	0.188	0.409	0.818	1.452	2.368	3.462	4.500	5.357
Pine, white	0.004	0.016	0.043	0.105	0.217	0.429	0.804	1.324	2.088	3.010	4.036	5.028	5.996
Pine, ponderosa	0.002	0.010	0.027	0.063	0.137	0.290	0.563	0.989	1.645	2.564	3.629	4.712	5.762
Pine, shortleaf	0.002	0.008	0.024	0.066	0.158	0.340	0.643	1.139	1.840	2.778	3.782	4.813	5.711
Pine, sugar	0.004	0.017	0.054	0.137	0.310	0.600	1.047	1.667	2.521	3.475	4.500	5.422	6.267
Redwood	0.004	0.019	0.058	0.144	0.346	0.818	1.636	2.813	3.982	5.233	6.122	6.818	7.323
Spruce, black	0.000	0.001	0.006	0.021	0.064	0.153	0.346	0.692	1.154	1.875	2.727	3.750	4.592
Spruce, Sitka	0.004	0.015	0.042	0.107	0.240	0.514	0.968	1.667	2.564	3.529	4.545	5.521	6.307
Hardwoods
Ash, black	0.006	0.039	0.148	0.429	0.947	1.800	3.000	4.500	5.625	6.716	7.438	7.965	8.257
Ash, white2	0.007	0.041	0.129	0.346	0.783	1.385	2.368	3.750	4.918	6.000	6.818	7.500	7.951
Aspen, bigtooth	0.000	0.004	0.022	0.081	0.243	0.563	1.286	2.250	3.462	4.839	6.000	6.870	7.500
Basswood2	0.002	0.051	0.188	0.474	0.947	1.636	2.432	3.462	4.592	5.556	6.383	7.031	7.589
Birch2	0.001	0.005	0.020	0.069	0.188	0.429	0.849	1.429	2.239	3.191	4.186	5.114	5.948
Birch, paper	0.000	0.004	0.018	0.064	0.161	0.375	0.750	1.343	2.250	3.333	4.500	5.625	6.429
Elm, American	0.005	0.045	0.250	0.750	1.636	3.000	4.091	5.294	6.475	7.317	7.826	8.182	8.443
Hickory2		0.003	0.041	0.257	0.720	1.500	2.903	4.286	5.521	6.569	7.317	7.826	8.182
Magnolia	0.002	0.007	0.018	0.044	0.098	0.202	0.419	0.783	1.360	2.278	3.435	4.712	5.902
Maple, sugar	0.001	0.007	0.028	0.129	0.346	0.783	1.429	2.308	3.383	4.455	5.357	6.207	6.839
Oak, northern red4	0.006	0.019	0.056	0.141	0.327	0.667	1.233	2.143	3.191	4.225	5.202	6.164	6.912
Oak, white	0.005	0.025	0.081	0.212	0.500	1.000	1.731	2.813	3.982	5.233	6.294	7.087	7.692
Walnut, black	0.002	0.009	0.034	0.100	0.247	0.545	1.023	1.765	2.778	3.930	5.202	6.040	6.839
Exotic hardwoods
Philippine mahogany	0.031	0.129	0.391	1.000	2.000	3.600	4.737	6.000	7.031	7.692	8.108	8.411	8.612
Sweetgum	0.002	0.014	0.043	0.109	0.254	0.529	0.989	1.636	2.521	3.586	4.663	5.625	6.438
Tupelo, black4	0.003	0.007	0.018	0.049	0.122	0.316	0.692	1.324	2.394	3.913	5.325	6.569	7.383
Yellow-poplar	0.004	0.011	0.028	0.071	0.168	0.346	0.600	1.047	1.676	2.557	3.673	4.813	5.711
Khaya	0.002	0.006	0.014	0.033	0.071	0.141	0.257	0.474	0.783	1.282	1.978	2.821	3.734
Mahogany (Swietenia)	0.004	0.013	0.039	0.102	0.231	0.474	0.947	1.698	2.778	4.036	5.233	6.250	7.092

You can also Download the Excel spreadsheet of this data

Note that cheap moisture meters don't even allow you to specify the wood species that is being measured. This causes a little bit of inaccuracy in the meters, but not too much. If you look at the resistance table (first table in this article), you will see that even though the resistance between species varies a lot, if you take a specific resistance and look it up in each row of the table, the closest values tend to be in the same or adjoining columns. So even if you get the species wrong, this will only result in an error of about one or two percent.

I used the above table to do a few spot check comparisons with my cheap meter, and they come out pretty close. Though realistically, I think I'd trust my method more than the cheap moisture meter.