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 neighbors 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.
Which input can actually move the answer
Square footage is the only figure in the form that sets the size of the answer; everything else multiplies it. That makes the five selectors easy to rank honestly, because each one's influence is just the ratio between its largest and smallest option — and those options are printed in the page you are reading, so the ranking is not a matter of opinion.
| Selector | Range of options | Most it can move the answer |
|---|---|---|
| How you heat | 0.2 – 1.0 | 5.00× |
| Appliance efficiency | 1.0 – 4.7 | 4.70× |
| Winter climate | 0.7 – 1.6 | 2.29× |
| Wood type | 1.0 – 1.5 | 1.50× |
| Insulation | 0.85 – 1.25 | 1.47× |
Two things fall out of that ordering. The first is that how you burn and what you burn it in swamp everything else. Moving from occasional weekend fires to primary heat multiplies the pile by five. Swapping a modern stove for an open fireplace multiplies it by nearly as much again. Neither is a property of your house, your county, or your winter — both are choices, and between them they matter more than the other three selectors put together.
The second is a warning about the bottom of the table. Insulation comes last here at 1.47×, and that is emphatically not a claim that insulation barely matters. It is a statement about the options this page offers, which run only from a tight house to a drafty one and stop well short of the extremes a real building stock contains. Where a selector's range is narrow, its influence in this tool is narrow. Read the column as "how much this page lets it move," not as "how much it matters."
Multiply the extremes together and the five selectors span a factor of 118. The same 1,800 square feet runs from about 0.3 cords — mild winter, weekend fires, tight house, good stove, dense hardwood — to roughly 39 cords for a severe winter heated primarily through an open fireplace in a drafty house on softwood. The second of those is not a firewood plan; it is the tool telling you the fireplace is the problem. But it explains why square footage alone predicts almost nothing, and why any page that answers "how many cords for a 1,800 square foot house" with a single number is guessing.
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 the water actually costs, in BTU
"The energy comes out of the fuel" is the right idea stated too vaguely to plan with, so here is the number. The USDA Forest Service's Forest Products Laboratory publishes a stack-loss formula for exactly this, and per pound of water in the wood it charges three separate things: 970 BTU to turn that water into steam, plus (212 − fuel temperature) to bring the water up to boiling first, plus 0.46 × (stack temperature − 212) to superheat the resulting steam on its way up the flue.
Run it with firewood entering the stove at 70°F and a stack temperature of 400°F: 970 + 142 + 86.48 comes to about 1,198 BTU per pound of water. The latent heat everyone quotes is only 81 percent of the real loss — the rest is heating the water and then heating the steam. Those two temperatures are assumptions, and they matter: hold the fuel at 70°F and swing the stack from 300°F to 600°F and the figure moves from about 1,152 to about 1,290 BTU per pound.
On the 970 itself, NIST's steam properties put saturated vapor at 1,151.1 BTU per pound and saturated liquid at 180.33 BTU per pound at 212°F, and the difference is 970.8. NIST prints the two enthalpies rather than the difference, and the Forest Products Laboratory prints 970 inside its formula rather than labeling it, so this is two sources agreeing on a value neither publishes as a standalone constant. Both are specific to 212°F at roughly one atmosphere.
Two different percentages, both called "moisture content"
This is the trap in the entire subject, and it is why two honest sources will describe the same firewood with different numbers. Moisture content can be water weight divided by total weight, or water weight divided by oven-dry wood weight. The first is the wet or "as fired" basis and can never exceed 100 percent. The second is the dry basis and routinely does.
The sources split cleanly along that line. The Forest Products Laboratory's stack-loss paper requires "that moisture content be expressed on the wet weight basis," and its Fuel Value Calculator table is footnoted "Wet basis." The same laboratory's Wood Handbook defines moisture content against "the mass of the ovendry wood" — dry basis. University of Missouri Extension writes that "freshly cut Missouri hardwoods commonly have a 75 percent moisture content on an oven-dry basis." Convert with wet = dry ÷ (1 + dry): Missouri's 75 percent dry basis is 42.9 percent wet basis, and the Utah State figure this page already cites — 50 percent or more water by weight, a wet-basis statement — is 100 percent on the dry basis. A percentage that sounds impossible is usually just a percentage quoted on the other basis.
Which matters most at the moisture meter, because pin meters are conventionally scaled on the dry basis. A reading of 20 percent is 16.7 percent wet basis. Feed the meter's 20 straight into a wet-basis formula and you overstate the water, and so the penalty, by about a fifth. Where this page and the seasoning advice above say "20 percent or less," that is the meter's number on the dry basis — the one you will actually be holding in the woodshed.
What it comes to per ton
The Forest Products Laboratory's Fuel Value Calculator publishes the whole picture in one table, per ton of wood as fired, gross against net — net being what survives after the water and the combustion chemistry take their cut:
| Wood, moisture content (wet basis) | Gross BTU per ton | Net BTU per ton |
|---|---|---|
| Green, 50% | 8,600,000 | 5,740,000 |
| Air-dried, 20% | 13,760,000 | 10,560,000 |
| Oven-dried, 0% | 17,200,000 | 13,800,000 |
Green wood at 50 percent delivers 46 percent less usable heat per ton than air-dried at 20 percent. That is the wet-wood penalty, published rather than modeled. One caution on carrying it across to a woodpile: the table is per ton, and firewood sells by the cord. A cord of green wood weighs more than a cord of the same species seasoned, because the water is extra weight riding along inside the same 128 cubic feet, so the per-ton gap and the per-cord gap are not the same number.
The last row is the one worth staring at. At zero moisture content, net heat still comes in 19.8 percent below gross. Water is not the only reason net trails gross: burning the hydrogen in wood creates water, which then has to be evaporated and superheated on exactly the same terms as the water the tree brought with it, and the Forest Products Laboratory charges that as a second, separate stack loss. Seasoning your wood perfectly does not retire that cost. Anyone telling you moisture explains the entire gap between a species' rated heat value and what your house actually feels is skipping the chemistry.
What each species is worth at the same price
The species table above is usually printed and then left alone. It is more useful turned into money. Because a cord is a fixed 128 cubic feet no matter what is in it, the heat column converts directly into a price: divide dollars per cord by million BTU per cord and you get the only figure that lets two loads argue fairly. Everything in this section is arithmetic on the table above — no outside prices or constants are introduced, and $300 a cord is used purely as a common yardstick.
| Species | $ per million BTU at $300/cord | Price that equals white oak at $300 |
|---|---|---|
| White oak | $10.31 | $300 |
| Sugar / hard maple | $11.76 | $263 |
| Red oak | $12.20 | $254 |
| American elm | $15.00 | $206 |
| Quaking aspen | $16.48 | $188 |
| Ponderosa pine | $18.52 | $167 |
| Cottonwood | $18.99 | $163 |
The right-hand column is the one worth carrying to a phone call. It is the most you can pay for that species and still be getting white oak's value for money. Cottonwood has to be 46 percent below the oak price merely to break even — $163 against $300 — and ponderosa pine has to be 44 percent below. Elm needs 31 percent off. Even sugar maple, a wood nobody apologises for, needs 12 percent.
Which turns the page's earlier warning into a number. A cord of cottonwood offered at ten percent below oak — $270 against $300 — costs $17.09 per million BTU where the oak costs $10.31. That is 66 percent more money for the same heat, dressed as a discount. The seller was not necessarily being dishonest; a cord really is a cord, and the volume really was delivered. The unit is simply the wrong one to shop in.
Note also how the table clusters. The top three species average 26.4 million BTU per cord and the bottom three average 16.7 — a gap of 1.58 times — while inside each group the differences are small. Ponderosa pine and cottonwood are within three percent of each other. Quaking aspen and American elm are within ten percent. Fussing over which oak you are getting is worth far less than knowing whether you are getting oak at all.
The two ambiguities compound
The face-cord problem and the species problem are usually discussed separately. They multiply. A "face cord" can legitimately mean a stack one stick deep at anywhere from twelve to twenty-four inches, which is a factor of two in volume. Species swing the heat inside that volume by a factor of 1.84, white oak to cottonwood. Put the worst case beside the best and the same three words — a face cord of firewood — describe deliveries of 3.95 million BTU (twelve-inch cottonwood) and 14.55 million BTU (twenty-four-inch white oak). That is a factor of 3.7, for an order placed in identical language at, quite plausibly, an identical price.
This is the strongest argument on the page for doing two boring things before money changes hands: get the piece length in inches, and get the species by name. Neither requires a tape measure, an argument, or any expertise. Both are questions a seller can answer in four words, and together they remove almost all of the range above.
What a season's wood needs in wall space
One last piece of arithmetic on the 128 cubic feet, because it catches people out every autumn. Stacked the classic way — four feet high, four feet deep — a cord is only 8 feet of row, and five cords fit in 40 feet. But almost nobody stacks four feet deep against a wall or under an eave. Stack a single rank of sixteen-inch pieces four feet high and the cross-section drops to about 5.3 square feet, so one cord needs 24 feet of wall and a five-cord winter needs 120 feet of it.
A hundred and twenty feet is not a woodshed; it is a fence line. Run the season estimate above, then decide the stacking depth before deciding where the wood goes — because the depth you can actually build is what sets how much wall you need, and it is the constraint people discover in November rather than in July.
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 labor, 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.
How much wood is in a cord? A full cord is a tightly stacked pile measuring 4 ft × 4 ft × 8 ft — 128 cubic feet of wood, bark, and air. It is the only legally defined firewood measure in most states.
What is a face cord or rick of wood? A face cord (or rick) is a stack 4 ft high and 8 ft long but only one stick deep — usually 16 inches. A 16-inch face cord is about one-third of a full cord.
How many cords of wood to heat a house for winter? A typical 1,500–2,000 sq ft home heated primarily with wood burns roughly 3–5 full cords of seasoned hardwood in a moderate climate, and 5–7+ in cold northern climates. Supplemental or occasional burning needs far less — often 1–2 cords.