A list with specific gravity values for North American trees can be found at the bottom of the page.

Specific Gravity

Basic Specific Gravity (based on oven-dry weight and green volume).

For the calculations, we use the basic specific gravity of the species. Based on this SG value, the dry density of the wood is calculated.

Cubic Metre Volume

Measure the stack's length, height and width in metres, and then multiply the length, height and width to get the cubic metre volume.
1 metre high stack x 1 metre wide stack x 1 metre in length stack = 1 cubic metre
a 2-metre high stack x 0.5-metre wide stack x 1 metre in length stack = 1 cubic metre or any other size that adds up to one cubic metre.

one stacked cubic metre of firewood contains, on average, 0.7 metres of solid wood
one cubic metre equals about 35.3 cubic feet of stacked firewood
3.6 cubic metres equals 128 cubic feet cubic feet of stacked firewood (a cord of firewood including the voids)
2.4 cubic metres = 85 cubic feet (a neatly stacked cord of firewood contains on average about 80 to 85 cubic feet of solid wood)

Btu's

The calculation in the calculator is based on Btu's per pound.

On average, one pound of oven-dried wood @ 0% MC can produce 8600 Btu's, The Gross Heating Value.

One pound of oven-dried wood for highly resinous species @ 0% MC can produce 9000 Btu's, The Gross Heating Value.

Loss due to moisture from the combustion of hydrogen reduces this amount of Btu's by about 6%
8600Btu's - 6% = 8084 Btu's. Net Heating Value
9000 Btu's - 6% = 8460 Btu's. Net Heating Value

The calculator will convert this to the right Btu's to calculate for kilograms.
1 Btu/pound = 2.204623 Btu/kilogram

Moisture Content (MC %)

The moisture in the wood will affect the available amount of Btu's.
1 lb of oven dry wood @ 0%MC contains 1 lb of wood, 0 lb water. Btu's generated = 8084 per pound
@ 70% MC 0.588 of wood and 0.412 water. Btu's generated = 8084 * 0.588 = 4753 Btu's
@ 20% MC 0.833 lb of wood and 0.167 lb water. Btu's generated = 8084 * 0.833= 6734 Btu's
Burning water is a waste of energy and money!