How the firewood estimate works
The season estimate begins from a planning baseline of one full cord of seasoned dense hardwood per 650 square feet of heated space, assuming wood does most of the heating, a moderate winter, and a modern stove. Everything after that is a multiplier. Colder winters push the number up. Tighter insulation pulls it down. Burning only on evenings or weekends cuts it sharply. A less efficient appliance raises consumption, because a larger share of the fuel's energy leaves up the flue instead of arriving in the room — an open masonry fireplace sits so far down that scale that the tool flags it rather than pretending it is a whole-house heater.
Those multipliers are our own planning assumptions rather than published constants, which is why the answer appears as a band instead of a single figure. Two neighbours with identical square footage routinely differ by a cord or more, because thermostat habits, window area, ceiling height, and how often the door swings open all matter, and none of them appear among the inputs.
A worked example
Leave the form at its defaults — 1,800 sq ft, moderate climate, primary heat, modern stove, average insulation, dense hardwood — and the arithmetic runs 1,800 ÷ 650 ≈ 2.8 cords at the midpoint, shown as a planning range of 1.8–3.9 full cords. The page reports that midpoint as roughly 8.3 sixteen-inch face cords and about 354 cubic feet stacked: a row 23 feet long, 4 feet high, 4 feet deep. Pacing off 23 feet in the yard is usually the moment the number stops being abstract and starts being a woodshed problem.
What a full cord actually is
A full cord is 128 cubic feet of wood stacked so the pieces lie parallel and touching — traditionally 4 ft high by 4 ft deep by 8 ft long. It is a measure of stacked volume. It is not a measure of weight, of heat, or of how many pieces you receive. Bark and the air gaps between splits live inside those 128 cubic feet, which is precisely why the shape and handling of a load change what you end up with.
Face cords, ricks, and truckloads
The terms sellers actually use are not defined units. A face cord, or rick, is 4 ft high and 8 ft long — 32 square feet of stack face — but only one piece deep, and nobody has agreed how deep a piece is. At 16 inches that stack is a third of a cord; at 12 inches a quarter; at 24 inches a half. One word, deliveries differing by a factor of two. A truckload is worse, since it describes a vehicle rather than a quantity: a half-ton pickup with a level bed carries a fraction of what a dump trailer carries, and both get called the same thing. Convert to full cords before comparing prices. A $120 rick of 16-inch wood works out to $360/cord, which tends to read differently from the way it was quoted.
Measuring a delivered stack
Stack the delivery, or watch it stacked, then take three measurements with a tape: the length of the row, its height, and the average length of the pieces. Multiply length by height by piece length in feet and divide by 128. Suppose the row measures 16 feet long and 4.5 feet high, with pieces averaging 18 inches: 16 × 4.5 × 1.5 = 108 cubic feet, and 108 ÷ 128 = 0.84 cords. Pay $300 for what was called a cord and your real price is about $356 per cord. Sample the height at several points and average it, because stacks slump and the tall end is never representative. The heat cost calculator includes a cord checker that runs this same arithmetic and then sets the result against propane, natural gas, fuel oil and a heat pump.
Stacking and piece shape change what fits
Two loads of identical timber can occupy visibly different stacked volumes. Unsplit rounds nest poorly and leave large voids; split wood with flat faces beds down tighter, so a cord of splits holds more solid wood than a cord of rounds. Straight, uniform lengths stack closer than short crooked pieces full of knots and crotch wood. Wood tipped into a heap, or crisscrossed for airflow, takes up far more space than the same wood laid in ranks — which is why the definition specifies stacked wood, and why a seller who dumps a pile in the driveway and calls it a cord has told you nothing you can check. If a load arrives loose, stack it, measure it, and settle the price afterwards.
Species matters more than volume
Because a cord is a volume, buying a cord tells you nothing about the heat you bought. Dense hardwoods pack far more energy into the same 128 cubic feet than light softwoods, and across common firewood species the spread approaches two to one. Utah State University Forestry Extension publishes heat content per cord of dry wood:
| Species | Million BTU per cord (dry) |
|---|---|
| White oak | 29.1 |
| Sugar / hard maple | 25.5 |
| Red oak | 24.6 |
| American elm | 20.0 |
| Quaking aspen | 18.2 |
| Ponderosa pine | 16.2 |
| Cottonwood | 15.8 |
A cord of white oak and a cord of cottonwood are an identical purchase by volume and nearly double the heat apart. Cottonwood offered ten percent below oak is not a bargain. This is also why "mixed hardwood" deserves a discount as a description: it can mean oak and hickory, or it can mean elm, box elder, and whatever blew down last spring. The wood-type selector above applies the same logic in reverse, raising the cord count when the species carries less energy per stack.
Those are heat values for the wood itself, with no appliance efficiency baked into them. Some circulated tables publish "available" heat per cord with a stove efficiency already applied; multiply one of those by your own stove figure and you have taken the discount twice. The heat cost page uses this same Utah State table to turn dollars per cord into dollars per million BTU delivered, applying efficiency exactly once, which is the only form in which a woodpile and a propane invoice can argue fairly.
Moisture and seasoning
Utah State notes that green firewood may contain 50 percent or more water by weight, and recommends air-drying before burning. That water must be evaporated inside the firebox before the wood burns properly, and the energy to do it comes out of the fuel rather than out of the woodlot — so a heat value measured on dry wood is simply not what green wood delivers. Seasoned means roughly 20 percent moisture or less, read on a freshly split face rather than on the weathered outside of a piece.
Getting there means splitting first, since bark resists drying, then stacking off the ground on pallets or rails with rows spaced for air movement and only the top covered, so rain sheds while the sides breathe. Six to twelve months suits most species; oak and elm often want a year or longer. A cheap moisture meter ends the argument about whether a pile is ready. One boundary worth naming: how a stove or insert is installed, and what clearances it requires, are questions for the appliance manual and your local code, not for a calculator.
What this tool cannot tell you
It cannot tell you what winter you are going to get. It cannot see your glazing, your ceiling height, your thermostat discipline, or whether somebody in the household likes the stove roaring. It does not know whether your wood is genuinely dry, and moisture shifts the answer more than most of the inputs do. It cannot price your labour, the saw, the splitter, the fuel to fetch it, or the Saturdays. And it certainly cannot verify what came off the truck — only a tape measure does that.
Buy or cut toward the top of the range. Seasoned wood still standing in April is not waste; it is next season's head start, and it is the only wood you own that is guaranteed dry.
Frequently asked questions
How long does a cord of wood last? It depends so heavily on house, stove, weather, and wood that any fixed answer misleads — divide your seasonal estimate above by the length of your burning season instead. A home burning 4 cords across a 5-month season averages roughly 3 weeks per cord through the cold months, and less than that during a genuine snap.
Is it cheaper to heat with wood? Usually yes if you cut your own; often close to break-even if you buy seasoned hardwood at market prices. Run your actual numbers on the heat cost calculator before assuming either way — the real arguments for wood are resilience during outages and a price that does not spike with the weather.