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Firewood Calculator

Use this free firewood calculator to find out how much wood is in a stack. Measure the length, height, and depth of the stack, pick the log length and the species, and the calculator works out the volume in cords and face cords, the approximate weight, and how much heat the wood will give. It is the quickest way to check that a delivery is really a full cord, to plan how much to order for winter, and to compare prices between sellers who quote different stack sizes.

How it works

Firewood is sold by volume, and the standard unit is the cord. One full cord is 128 cubic feet of stacked wood — traditionally a stack 8 feet long, 4 feet high, and 4 feet deep. The calculator finds your stack's volume by multiplying length times height times depth, then divides by 128 to get cords. An 8-by-4-by-4 stack is exactly 128 cubic feet, so it is exactly one cord. A stack half that size is half a cord, and a stack twice as long is two cords. The math is simple; the hard part is measuring honestly, because a stack that is 8 feet long and 4 feet high but only 3 feet deep is three-quarters of a cord, not a full one.

The face cord is where most confusion — and most short deliveries — happen. A face cord is a stack 8 feet long and 4 feet high, but only one log length deep. With 16-inch logs, one face cord holds about 42.7 cubic feet, so three face cords make one full cord. With 24-inch logs, a face cord holds 64 cubic feet, so two make a cord. With 12-inch logs, it takes four face cords to make a cord. That is why the calculator asks for log length: the same 8-by-4 face can be a very different amount of wood depending on how long the logs are. If a seller quotes a price per face cord, always ask the log length before comparing it with a price per cord.

Weight and heat depend on species. Dense hardwoods pack more wood fiber into every cubic foot, so they weigh more and burn longer and hotter. Hickory is the heaviest and hottest common firewood at about 4,000 pounds and 27 million BTU per cord, followed by oak at about 3,800 pounds and 24 million BTU. Maple, ash, and birch sit in the middle at roughly 20 to 22 million BTU per cord, while softwoods like pine weigh only about 2,200 pounds per cord and give about 15 million BTU. Pine lights easily and makes good kindling, but it burns fast and leaves more creosote in the chimney, so it is rarely the best choice as a main heating wood.

Seasoning changes both weight and heat. Green wood fresh from the tree can be half water by weight, so a green cord weighs roughly 40 percent more than the same wood seasoned — and much of its heat goes into boiling that water away instead of warming the room. This calculator multiplies the weight by 1.4 and the usable heat by 0.8 for green wood. Properly seasoned wood has dried for six to twelve months under cover, with the ends exposed to air, until its moisture is below about 20 percent. It feels light for its size, the ends show cracks, and two pieces knocked together make a sharp hollow sound instead of a dull thud.

To measure a stack, run a tape along the full length at the base, measure the height at several points and average them — stacks sag in the middle and lean at the ends — and measure the depth as the average log length if the logs are cut evenly. If the stack is round, like a pile in a ring, or the logs are different lengths, measure in sections and add the sections together. For a loose pile that has not been stacked, the same volume holds roughly a third less wood because of the extra air, so divide the pile's rough volume by 128 and then multiply by about 0.7 as a planning figure.

When a delivery arrives, measure before the wood is unloaded if you can, or stack it neatly and measure the finished stack. A seller who delivers loose in a truck bed is not delivering stacked cords — a pickup bed heaped with wood is typically a third to a half of a cord, depending on the bed size. Paying by the cord and verifying with a tape measure is the simplest protection against short loads, and it is also how you learn your own burn rate: note the date a stack is finished and how many cords the next one holds, and after one winter you will know your household's real number.

Worked example

A delivered stack measures 8 feet long, 4 feet high, and 4 feet deep, cut into 16-inch logs of seasoned oak.

Step 1: Volume — 8 × 4 × 4 = 128 cubic feet.
Step 2: Cords — 128 ÷ 128 = 1.00 cord.
Step 3: Face cords — one face cord at 16 inches is 8 × 4 × (16 ÷ 12) = 42.67 cubic feet, so 128 ÷ 42.67 = 3.00 face cords.
Step 4: Weight — 1.00 cord × 3,800 lb per cord = about 3,800 lb.
Step 5: Heat — 1.00 cord × 24.0 million BTU per cord = about 24.0 million BTU.

The stack is exactly one full cord of seasoned oak: 3 face cords, about 3,800 pounds, and about 24 million BTU of heat — enough to heat a well-insulated room for several cold weeks of evening fires.

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