What a cord is, by law
A cord is a legal unit of volume, not a rough local custom. The definition comes from section 2.4 of the Uniform Regulation for the Method of Sale of Commodities in NIST Handbook 130 (2016 edition, as reproduced by Connecticut): a cord is "the amount of wood that is contained in a space of 128 cubic feet when the wood is ranked and well stowed." The same section spells out what ranked and well stowed means: the pieces are placed in a line or row, with individual pieces touching and parallel to each other, and stacked in a compact manner.
That wording is why the calculator asks for the outside dimensions of a stack rather than the size of each log. The 128 cubic feet is the space the stacked wood fills, gaps included, so you measure the stack the way you would measure a box. Nebraska has adopted that regulation into law by reference, and Washington's Department of Agriculture, which adopts Handbook 130 as the state's legal method of sale in chapter 16-662 WAC, puts the test in one line: if the width times the height times the length equals 128 cubic feet, you have a cord.
In metric terms, NIST Special Publication 811 lists one cord (128 cubic feet) as 3.624 556 cubic metres. Handbook 130 allows fireplace and stove wood to be sold by the cord and fractional parts of a cord or by the cubic metre, so the calculator shows both.
How to measure your stack
Stack first, then measure. The Nebraska Department of Agriculture's buyer leaflet, published with the National Conference on Weights and Measures, says to ask the seller to stack the wood when it is delivered (you may have to pay extra for this) or to stack it yourself, and to measure it before using any. Stack the pieces in rows, parallel and touching, with as few gaps as possible.
Take three measurements. Length is the run of the stack along the ground. Height is from the ground to the top of the stack. Depth is the front-to-back distance, which for a single row is the length of the pieces themselves; a row of 16 in pieces is 16 in deep. If the top of the pile is uneven, a few height readings along the run, averaged, give a fairer figure than the tallest point.
Enter length and height in feet and depth in inches, or switch to metres and centimetres. The default stack, 8 ft long, 4 ft high and 16 in deep, works out to 8 × 4 × 1.333 = 42.67 cubic feet, which is 42.67 ÷ 128 = 0.333 of a cord. The extra line under the result tells you how long the same stack would need to run to hold one full cord: at 4 ft high and 16 in deep that is 128 ÷ (4 × 1.333) = 24 ft.
Stacking style matters as well as size. Washington's Department of Agriculture notes that wood stacked in a crisscross or log cabin fashion is secure and will stand freely, but it does not meet the legal definition, and most likely contains less wood than a stack laid by the parallel method. If your delivery arrived as a loose heap or a crisscrossed pile, restack it before you measure, or the number on the screen will be bigger than the wood you actually have.
The same cord in different shapes
Any stack whose three dimensions multiply to 128 cubic feet is a cord. The Nebraska leaflet draws two of them: 4 ft × 4 ft × 8 ft, and 2 ft × 4 ft × 16 ft. The first is two 2 ft deep rows side by side, or one row of 4 ft logs; the second is a single row of 2 ft pieces stacked 4 ft high and 16 ft long.
Washington's guidance offers a quick way to picture the first shape: imagine a 4 ft by 8 ft space filled with wood to a height of 4 ft, and note that most long-bed pickup trucks have beds close to 4 ft by 8 ft. That is a visual check, not a measurement. A bed of that footprint stacked level to 2 ft holds 4 × 8 × 2 = 64 cubic feet, half a cord, so a bed of that size holds a full cord only when the wood is stacked about 4 ft high.
For metric stacks the arithmetic is the same with a different divisor. A stack 2.4 m long, 1.2 m high and 40 cm deep holds 1.152 cubic metres, which is 1.152 ÷ 3.624 556 = 0.318 of a cord, or about 40.68 cubic feet. Switch the unit control to m / cm and the calculator does the conversion for you.
Words a seller is not allowed to use
Handbook 130 section 2.4.4 says the terms face cord, rack, pile, truckload, or terms of similar import shall not be used when advertising, offering for sale, or selling wood for use as fuel. Washington's guidance gives the reason: these terms have no legal definition, so they cannot be used as a measure of how much firewood is being sold. The Nebraska leaflet treats a seller who uses them as a warning sign of a possible problem.
This matters when comparing offers. A price quoted for a face cord or a rack tells you nothing you can check, because the depth is not fixed. Ask for the quantity as a cord or a fraction of a cord, then use the calculator on the stack you receive. If you know the price per full cord, enter it and the tool prices the stack you measured; a third of a cord at $300 per cord should cost $100.
There are a few exceptions in the same section. Natural wood sold in packages smaller than 0.45 cubic metres (1/8 cord or 16 cubic feet) is labelled in litres, cubic inches or cubic feet rather than as a fraction of a cord, and the calculator flags any stack under that size. Artificial compressed logs are sold by weight when sold singly and by weight plus count when packaged, pellets and chips no larger than 6 in in any dimension are sold by weight, and packaged wood flavoring chips in amounts under 0.45 cubic metres (1/8 cord) are labelled in litres, cubic inches or cubic feet.
Check the delivery ticket
Handbook 130 section 2.4.5 requires a delivery ticket or sales invoice whenever nonpackaged fireplace or stove wood is sold. It must show the vendor's name and address, the purchaser's name and address, the delivery date, the quantity delivered and the quantity the price is based on if those differ, the price of the amount delivered, and the identity of the wood in the most descriptive terms commercially practicable. Washington's guidance adds two habits of its own: write down the seller's phone number and the licence plate of the delivery vehicle.
Type the quantity on the ticket into the optional field and the calculator compares it with your measurement. Suppose the ticket says one cord and the stacked wood measures 8 ft long, 4 ft high and 3.5 ft deep. That is 112 cubic feet against the 128 billed, so the tool reports 16 cubic feet short, 12.5% of what you paid for.
If a ticket names the species, section 2.4.2 requires the stated percentages of each species group to be accurate within 10 percent; the handbook's example is 50 percent hickory, 50 percent miscellaneous softwood.
If the stack comes up short, both state sources give the same order of steps: contact the seller before you burn any of the wood. The Nebraska leaflet says that if the seller can't or won't correct the problem, contact your state weights and measures authority, and that a photograph of the stacked wood helps document the shortage. Washington's department notes that, with limited resources, it can only investigate chronic and repeat violators.
Before you order
Measure the space where the wood will go before you order. If your rack or wall space is 12 ft long and 4 ft high and you burn 16 in pieces, a full cord will not fit in one row: the calculator shows a full cord at that height and depth needs 24 ft of run. Two rows of 16 in pieces, 32 in deep, would bring that down to 12 ft.
If you are building the rack yourself, this site's board foot calculator prices the lumber, and the square footage calculator handles a floor or pad under it.