Firewood Calculator: How Much Wood Is in a Cord?

The firewood formula

The calculator runs three lines of math:

• Cubic feet = length (ft) × height (ft) × piece length (in) ÷ 12 × rows
• Cords = cubic feet ÷ 128
• Row length for one full cord = 128 ÷ (4 × piece length (in) ÷ 12)

Dividing by 12 turns the piece length from inches into feet. The 128 is the size of a cord: NIST Handbook 44, from the National Institute of Standards and Technology, lists 1 cord of firewood as exactly 128 cubic feet, which equals 8 ft × 4 ft × 4 ft. The last line tells you how long a single row 4 ft high must be to make a full cord.

Worked example (the calculator's default values)

Say you have one row of firewood 8 ft long and 4 ft high, cut into 16 in pieces.

1. Piece length in feet: 16 ÷ 12 = 1.33 ft
2. Volume: 8 × 4 × 16 ÷ 12 = 42.67 cu ft, shown rounded as 43 cu ft
3. Cords: 42.67 ÷ 128 = 0.33 cord
4. One full cord in a single 4 ft high row: 128 ÷ (4 × 16 ÷ 12) = 24.0 ft

The calculator shows the same result: "Your stack holds about 0.33 cords (43 cu ft). A full cord is 128 cu ft, for example a stack 8 ft long, 4 ft high and 4 ft deep. With 16 in pieces, one row 4 ft high has to run 24.0 ft to make a full cord."

Change the rows to 3 and the stack becomes 48 in (4 ft) deep: 8 × 4 × 16 ÷ 12 × 3 = 128 cu ft, or 1.00 cord. That is why three 8 × 4 ft rows of 16 in wood make one full cord.

The optional fields add to the same result. If that single row had been sold to you as a full cord, enter 1 in Cords ordered and the calculator adds: "That is 33% of the 1 cord you ordered (128 cu ft): about 85 cu ft (0.67 cords) short." Pick red oak as the species and it adds about 8.2 million BTU of heat and 1,176 lb, from Utah State Extension's figures for air-dried wood.

Firewood cord chart by piece length

Every row in this chart is 4 ft high. The numbers are straight volume math.

This matches what extension services report. Penn State Extension says a face cord is generally 16 in deep and holds 1/4 to 1/2 of the wood in a cord, and Utah State University Extension puts a face cord at 32 to 48 cu ft for the usual 12 to 18 in pieces.

Cord dimensions: full, half, and face cord

How big each unit is with the wood stacked tight, the way a cord is measured, plus a loose cord and a pickup load for comparison. A full cord is 128 cu ft under NIST Handbook 44; the half cord dimensions are Montana State Extension's, the rick is often treated as a third of a cord, per University of Kentucky forestry specialists, the loose cord is Maine's definition, and the pickup figure is Utah State Extension's.

Cord vs. face cord, rick, and other terms

Only the cord has a fixed size. The other names describe the face of a stack, not its volume, so two sellers can use the same word for very different amounts of wood.

• Full cord: 128 cu ft, usually 8 ft long × 4 ft high × 4 ft deep.
• Half cord: 64 cu ft, which Montana State Extension describes as 4 ft deep, high, and long.
• Face cord: 4 ft high and 8 ft long, but only as deep as the pieces are long, per Utah State Extension.
• Rick or fireplace cord: often treated as one-third of a cord, though University of Kentucky forestry specialists note regional differences.
• Pile, truckload, or pickup load: Montana State Extension warns that these can vary greatly in size.

Face cord and rick dimensions

A face cord is 8 ft long and 4 ft high, and only as deep as the pieces are long. With 16 in pieces that is 8 × 4 × 16 ÷ 12 = 42.67 cu ft (about 43), one-third of a 128 cu ft cord. With 12, 18, and 24 in pieces it is 32, 48, and 64 cu ft, as the chart above shows.

A rick has no fixed dimensions. University of Kentucky forestry specialists say a rick and a fireplace cord are often regarded as one-third of a cord, the same 42.67 cu ft as a face cord of 16 in wood, though regional differences occur. Nor is it a legal unit of sale: the NIST Handbook 130 model regulation that Connecticut's rules below are taken from says firewood is sold by the cord, fractions of a cord, or the cubic meter (small packages and pellets aside), and bars "face cord," "rack," "pile," "truckload," and "terms of similar import." University of Missouri Extension and the Hamilton County, Ohio, Auditor's weights and measures division name the rick among the terms not to use. If a seller quotes a rick, ask for the length, height, and piece length behind it.

State rules vary: Connecticut as an example

Firewood sales fall under state weights and measures rules, which are not the same everywhere. Connecticut's Department of Consumer Protection publishes a clear example, taken from NIST Handbook 130:

• A cord is the amount of wood in 128 cu ft "when the wood is ranked and well stowed."
• Firewood is sold by the cord, fractions of a cord, or the cubic meter.
• The terms "face cord," "rack," "pile," "truckload," and similar terms may not be used to advertise, offer, or sell firewood.
• The delivery ticket must show the seller's and buyer's names and addresses, the delivery date, the quantity delivered, the price, and a description of the wood.

University of Missouri Extension likewise states that firewood must, by law, be sold by the cord or a fractional part of a cord, with a bill of sale. Other states may word things differently or allow terms Connecticut bans, so check with your state's weights and measures office.

How to check a delivery

1. Ask before you buy for the quantity in cords, plus the stack length, height, and piece length behind it.
2. Measure a tight stack. Missouri Extension advises against accepting a randomly piled load for measurement. If the wood will be dumped, agree up front that you will stack and measure it before paying.
3. Compare with the ticket. Run your measurements through the calculator with the cords on the ticket in Cords ordered, and keep the receipt until you have checked.
4. Report a short cord to your state weights and measures office. Connecticut's DCP, for example, invites complaints about "short" cords.

Tips for seasoning and storing firewood

• Give it time. The EPA's Burn Wise program says to season wood at least six months; its firewood brochure notes softwoods take about 6 months and hardwoods about 12. Penn State Extension gives 6 to 12 months, and Missouri Extension suggests ordering in the fall for next year.
• Test it. The EPA says wood burns best at less than 20 percent moisture and recommends a wood moisture meter. Seasoned wood is darker, weighs less, and sounds hollow when knocked against another piece. Penn State adds small end cracks, called checks, as a sign.
• Stack for airflow. The EPA suggests a single row, split side down, on rails off the ground. Penn State recommends a dry, sunny, windy spot.
• Cover the top only. Keep the sides open. Penn State warns that wrapping the whole stack in a tarp creates a tent that holds moisture in.
• Keep it away from the house. The EPA says to build the stack away from buildings, and Missouri Extension warns that wood piled against a house can discolor it and help termites get in.
• Don't hoard it. Missouri Extension suggests not keeping wood outside more than a year or two, because borers can cut a pile's weight by 20 to 30 percent a year.

How much firewood you need, and how much heat you get

How many cords of wood does it take to heat a house?

Roughly 2.7 to 3.3 cords per 1,000 sq ft in a cold northern climate, and 1 to 2 cords per 1,000 sq ft in a mild southern one, if wood is your main heat. UNH Cooperative Extension says a fairly weather-tight 1,500 sq ft house burns 4 to 5 cords of seasoned wood in an average New Hampshire heating season, and West Virginia University Extension says a 1,500 sq ft home might burn 4 cords of seasoned wood in an average heating season. Oklahoma State University Extension says 1 or 2 cords per 1,000 sq ft may be all you need in Oklahoma, and Iowa State University Extension puts average home-heating use in Iowa at 3 to 7 cords a year.

The UNH and WVU figures are for 1,500 sq ft and Oklahoma State's for 1,000 sq ft; the other rows scale them in proportion to floor area, so treat them as a starting point. Lean to the high end for a drafty house, a long winter, or light wood: white pine holds about 55 percent of white oak's heat per cord in the BTU chart below (15.9 vs. 29.1 million BTU). If wood supplies only part of your heat, scale down; half the heat takes roughly half the wood. To picture the pile, use the chart by piece length: 4 cords of 16 in wood is 12 face cords, or one row 4 ft high and 96 ft long.

The calculator's Cords for winter mode does this math for your floor area and region. Or enter the fuel your furnace burned last winter, and it turns that heat into cords: the U.S. Energy Information Administration puts a gallon of propane at 91,452 BTU, a gallon of heating oil at 138,500 BTU, and a therm of natural gas at 100,000 BTU. For example, 800 gallons of propane in an 80 percent efficient furnace delivered about 58.5 million BTU, the same heat as about 3.4 cords of red oak (24.6 million BTU per cord) in a wood stove at 70 percent efficiency, or 3.2 to 3.7 cords at 65 to 75 percent.

How much does a cord of firewood weigh?

It depends on the species and on how much water is still in the wood. Utah State University Extension lists these weights for a full cord, green (freshly cut) and after air drying:

Drying can cut a cord's weight roughly in half: cottonwood goes from 4,640 to 2,272 lb, while black locust loses only about 13 percent. A face cord of 16 in wood is one-third of a cord, so it weighs about one-third as much. Denser dry wood also holds more heat: the same table lists 29.1 million BTU per cord for white oak and 15.8 million for cottonwood. If wood supplements a furnace, the furnace size calculator estimates the heat the whole house needs in BTU per hour. If propane is the other fuel, EIA puts a gallon at 91,452 BTU, and the propane usage calculator shows how long a tank lasts.

Firewood BTU chart by species

How much heat a full cord holds, by species, from Utah State University Extension's firewood table, sorted from most to least. Both columns are for air-dried wood: the source gives the heat per cord of dry wood and the weight of a cord after air drying. Green wood yields less heat, because part of it goes into boiling off water.

How much of a cord's heat reaches the room

From 10 percent to 83 percent, depending on what you burn the wood in. The BTU chart shows the heat in the wood; the Department of Energy says new non-catalytic wood stoves are often 65 to 75 percent efficient and new catalytic stoves and inserts up to 83 percent, while Penn State Extension says an open fireplace is only 10 to 20 percent efficient at creating heat. The same cord, in million BTU of usable heat:

So heating with an open fireplace takes roughly 3 to 7.5 times as much wood as a modern stove for the same heat. The EPA adds that certified stoves use about one-third less wood than older ones for the same heat, and warns that an advertised efficiency is often combustion efficiency, which can run 10 to 20 percent above the overall figure.

Common mistakes to avoid

• Treating a face cord as a cord. With 16 in pieces it is a third of the wood. Always ask for the piece length.
• Mixing inches and feet. The piece length field is in inches. Typing 1.33 (feet) instead of 16 gives a result twelve times too small.
• Burning it green. Missouri Extension says burning green wood can cost 10 to 12 percent of its original heat potential.