What this calculator does: It compares the firewood your woodland could supply each year with the firewood you burn each year, and tells you whether you have a surplus or a shortfall and how many wooded acres your use would take. A second tool on the same page turns the height, width and length of a woodpile into cords.
Who it’s for: Homesteaders and rural landowners who heat with wood, or want to, and who own wooded land or are thinking about buying some. It also suits anyone who has bought a “cord” of wood and wants to check what they got.
The answer it produces: An estimated supply in cords per year, the annual use you entered, the difference between them, and the wooded acres needed to cover your use at your own assumptions. The stack tool gives the size of a pile in cords and cubic feet, and what share of a year’s use it covers.
Important limitation: The calculator does not work out how much firewood your house needs. You type in your annual use yourself. The supply figure is simply your acres multiplied by a yield you estimate and a harvest percentage you choose, so it is only as good as those guesses. It is not a forest inventory.
Compare Your Woodlot Supply With Your Wood Use
A standard cord is a stack measuring 4 feet × 4 feet × 8 feet, or 128 cubic feet.
How much wood do you have?
A conservative default, not a maximum. Actual sustainable yield varies enormously by forest type, region, and management goals.
How much do you use?
If you know your actual historical usage, that’s usually more reliable than a generic estimate.
Measure a Stack
A standard cord is 4 ft × 4 ft × 8 ft — 128 cubic feet. Enter your stack’s dimensions to see how many cords you have. For a “face cord” of 16-inch pieces, use 4 × 1.33 × 8, which is about one-third of a full cord.
Planning estimates only. Actual sustainable harvest depends on forest composition, growth rate, and management goals — consult a forester or your state/Cooperative Extension forestry program for a site-specific assessment.
How the Calculation Works
There are two separate tools, and each runs in your browser when you press its button. The supply tool takes three steps and the stack tool takes one.
- Estimated supply. Wooded acres × harvestable cords per acre per year × harvest percentage ÷ 100. Every field must hold a number of zero or more, and a blank or negative entry gets a message instead of a result.
- Balance. Supply minus the annual use you entered. A result of zero or more is shown as a surplus. A negative result is shown as a shortfall, with a note that you may need to source additional wood.
- Acres needed. Annual use ÷ (cords per acre × harvest percentage ÷ 100). This is the number of wooded acres it would take to cover your use at the same assumptions. If your use is zero, or the yield or harvest percentage is zero, the tool says so instead of showing a number.
- Stack measurement. Height × width × length, in feet, gives cubic feet. Dividing by 128 gives cords. The tool shows the answer to two decimal places, and if you entered an annual use above the tool also shows what percentage of a year’s use the stack covers. All three dimensions must be greater than zero.
Nothing in the supply calculation looks at your forest. It does not know the tree species, the age of the stand, the soil, the slope or how much of your land can be reached with a truck or a tractor. Those all sit behind the yield number you type in.
Inputs and Assumptions
| Input | Starting value | Notes |
|---|---|---|
| Wooded acres | 5 | Only the acres that can actually be harvested. Steep, wet, protected or inaccessible ground should not be counted. |
| Est. harvestable cords/acre/yr | 0.5 | Your estimate of what an acre can yield each year. It is a guess, not a measurement. |
| Conservative harvest % of that resource | 50 | The share of the estimate you plan to take. It is applied on top of the yield above. |
| Estimated annual firewood use (cords/year) | 4 | Placeholder. Your own record from a recent winter is better. Zero is allowed. |
| Stack height, width and length (ft) | 4, 4 and 8 | Measure the stack as it sits, in feet. |
And these are the assumptions built into the tool:
| Assumption | Value used |
|---|---|
| One cord | 128 cubic feet of stacked wood |
| Supply | Steady every year, at exactly the yield you enter |
| Use | Exactly the figure you enter |
| Not included | Forest type, tree growth, wood species, moisture, stove efficiency, insulation, climate, terrain, access, equipment and labor, cost, and wildlife or habitat goals |
Note that the default 0.5 cords per acre is cut again by the default 50% harvest share, so the starting values assume only 0.25 cords per acre per year. The University of Kentucky’s forestry extension says a typical woodland can produce about one third of a cord per acre per year when managed sustainably. The starting values are in a similar range, but they are a placeholder for your land, not a finding.
What the Result Means
- Estimated sustainable supply. The cords per year your woodland could provide if your yield and harvest percentage are right. The word “sustainable” describes what you entered. The tool does not check it.
- Your estimated use. Your own annual figure, shown back to you to two decimal places.
- Surplus or shortfall. The gap between the two. A surplus is a sign that your assumptions fit together, not a promise that you can cut that much. A shortfall means you need more acres, more efficiency, or wood from another source.
- Wooded acres needed. The acreage that would produce your annual use at your own yield and harvest percentage. Compare it with the acres you actually have and can reach.
- Stack size in cords. The stack’s volume divided by 128. This is a measure of the space the pile fills, which includes air gaps and bark. It is not a measure of solid wood. If you entered an annual use, the tool also gives the stack as a percentage of one year’s use.
Example Calculation
Using the starting values, 5 acres × 0.5 cords per acre × 50% = 1.25 cords a year. The tool shows this as 1.25. Against a use of 4 cords a year, the balance is 1.25 − 4 = −2.75, which the tool shows as a shortfall of about 2.75 cords. To cover 4 cords with those same assumptions the tool reports 4 ÷ (0.5 × 0.5) = 16.0 wooded acres.
Here is how three sets of inputs compare, using the tool’s two-decimal display:
| Scenario | Acres | Cords/acre/yr | Harvest % | Use | Supply | Result | Acres needed |
|---|---|---|---|---|---|---|---|
| Starting values | 5 | 0.5 | 50 | 4 | 1.25 | Shortfall of about 2.75 | 16.0 |
| Extension yield of about 1/3, all treated as sustainable | 10 | 0.33 | 100 | 3.5 | 3.30 | Shortfall of about 0.20 | 10.6 |
| Same yield, larger woodlot | 12 | 0.33 | 100 | 3.5 | 3.96 | Surplus of about 0.46 | 10.6 |
The second and third rows use the University of Kentucky’s figures of about 3.5 cords a year for a typical home and about one third of a cord per acre per year. The extension fact sheet reaches the same conclusion: a landowner needs a minimum of about 10 acres. Because that yield is already described as sustainable, these rows set the harvest percentage to 100 rather than cutting it a second time.
Measuring a stack. A pile 4 feet high, 4 feet wide and 8 feet long is 128 cubic feet, which is exactly 1.00 cord. A stack of 16 inch pieces that is 4 feet high and 8 feet long is only one piece deep. Enter 1.33 for the width and you get about 43 cubic feet, or 0.33 cords. The stack tool’s own note above the inputs gives the same 4 × 1.33 × 8 shortcut. That is the “face cord” that many sellers deliver. The University of Wisconsin Extension describes a face cord as 4 feet high and 8 feet wide, with pieces shorter than 4 feet, so its size depends on the length of the pieces.
A cord is not all wood. The Wisconsin fact sheet gives an average standard cord as about 62% solid wood, 28% air and 10% bark, or roughly 79 cubic feet of solid wood. Carefully stacked pieces can be much tighter, and one published measurement of a neatly stacked cord found 80% or more solid wood. Solid content changes with piece size, straightness, bark and how the pile settles as it dries, so two cords can hold different amounts of fuel.
How to Use the Result in a Real System
- Start with real use. Count the cords you actually burned last winter, or use the off-grid heating fuel calculator for a rough figure. Then adjust for winters that were milder or colder than usual.
- Be skeptical of the yield. Run the calculator with a low, a middle and a high yield, and see whether your plan survives the low one.
- Get a site-specific opinion. Your state forestry agency, a consulting forester or your Cooperative Extension office can tell you what your stand can produce and which trees to remove to improve it.
- Cut a year ahead. The EPA recommends seasoning wood for at least six months, and the University of Kentucky says one year is preferred. Wood cut this spring is next winter’s fuel at best.
- Store it properly. The EPA advises keeping wood outdoors, off the ground, with only the top covered, because covering the sides traps moisture. Kentucky’s fact sheet adds that stacks should sit 4 to 6 inches off the ground, out of shade and at least 30 feet from buildings.
- Test the moisture. The EPA says wood burns best below 20% moisture and recommends checking with a moisture meter.
- Plan for a gap. If the calculator shows a shortfall, options include buying seasoned wood, improving insulation and the stove, or adding acres. The land suitability calculator and the off-grid budget calculator can help with the land and money sides of that decision.
Important Variables That Can Change the Result
- Forest type and condition. Growth rates differ from stand to stand, and a healthy, well-managed stand generally produces more usable wood than a neglected or damaged one.
- Wooded acres you can really harvest. Wetlands, steep slopes, buffers along streams and inaccessible corners do not count.
- Wood species. The Kentucky fact sheet notes that hickory and Osage-orange can burn hotter than southern yellow pine and basswood, and that density matters more than a hardwood or softwood label. A cord of a dense species holds more heat.
- Moisture content. Wet wood gives less usable heat, which raises the number of cords you burn.
- Stove and house efficiency. A tight house with an efficient stove can burn far less than a drafty one with an old stove.
- Climate and how much you rely on wood. Wood as the only heat source burns much more than wood as a supplement.
- Harvest method. Thinning poor trees, using storm-fallen wood and taking healthy trees for firewood are very different for forest health.
- Stacking and piece length. Both change how much solid wood is in a cord.
Common Mistakes
- Treating the yield as a fact. The cords per acre field is an estimate. Change it and the result changes by the same proportion.
- Counting every acre. Only the harvestable, accessible part of a woodlot belongs in the acres box.
- Cutting the trees you can reach first. Taking the easiest, healthiest trees every year can leave the stand worse each time.
- Forgetting the drying time. Supply arrives green. It needs at least six months, ideally a year, before it burns well.
- Confusing a face cord with a cord. A face cord of 16 inch pieces is about one third of a standard cord.
- Entering use from an unusually mild winter. Plan on an average or cold winter, not the best one.
- Reading the stack result as solid wood. The 128 cubic feet of a cord includes air and bark.
- Burning the wrong material. The EPA warns against burning treated or painted wood, glued wood products, and wet, rotted or moldy wood, because it can release toxic chemicals and damage the appliance.
When This Calculator Should NOT Be Used
- To find out how much firewood your home needs. It has no climate, house or stove inputs. Use your own records or the heating calculator.
- To plan a timber sale or commercial harvest. That takes a forester and a real inventory.
- As a forest management plan. It does not consider growth, regeneration, wildlife, water or fire risk.
- To decide what is legal to cut. State, county and public land rules, and any conservation easements, come first.
- For a small yard with a handful of trees. The formula gives false precision at that scale.
- To size a stove or chimney. Those need the appliance maker’s specifications and a qualified installer.
Related Honey Hen Calculators
- Off-Grid Heating Fuel Calculator: estimate how much wood, propane or other fuel your heating may use.
- Homestead Land Suitability Calculator: score a property for homesteading.
- Off-Grid Budget Calculator: plan the cost of your off-grid systems.
- Off-Grid Readiness Quiz: see how your household scores across areas of self-sufficiency.
- All Homestead Calculators: the full set of planning tools in one place.
Related Honey Hen Articles
- Off-Grid Passive Solar Home Materials to Use
- Earth-Sheltered Homes Passive Solar Design
- Energy-Efficient Off-Grid Appliances: 10 Picks for Homesteads
Authoritative Sources
- University of Kentucky Cooperative Extension: Firewood (FORFS 17-11). Typical household use, sustainable yield per acre, seasoning, storage and wood species.
- University of Wisconsin Extension Forestry: Fact Sheet FEM 044 on Wood Measurement. Definitions of a cord and a face cord, and the solid wood content of a cord.
- U.S. EPA Burn Wise: Best Wood-Burning Practices. Seasoning time, moisture content, storage and what not to burn.
- Northern Woodlands: How Solid Is a Cord of Wood? A measured look at how much of a stacked cord is solid wood.
Firewood Calculator FAQ
How many cords of firewood do I need for a winter?
It varies widely. The University of Kentucky puts a typical home at about 3.5 cords to heat through winter, but climate, house size, insulation, stove efficiency, wood species, moisture and how much heat comes from wood all move that number. Your own record from past winters is the best guide. This calculator does not estimate it.
How much wood is in a cord?
A standard cord is 128 cubic feet of stacked wood, measured 4 feet high, 4 feet wide and 8 feet long. That volume includes bark and air spaces. The University of Wisconsin gives an average of about 79 cubic feet of solid wood, and tightly stacked wood can hold more.
How many acres of woods do I need to heat my house with wood?
The University of Kentucky says a typical woodland produces about one third of a cord per acre per year when managed sustainably, so a home using 3.5 cords needs a minimum of about 10 acres. A productive woodlot may need less and a poor one more. Ask a forester about your own stand.
What is a face cord?
A face cord is a stack 4 feet high and 8 feet long, made of pieces shorter than 4 feet. With 16 inch pieces it holds about a third of a standard cord. Ask a seller for the piece length and the stack’s dimensions, or enter them in the stack tool above.
How long does firewood need to season?
The EPA says at least six months, and the University of Kentucky says one year is preferred. Splitting the wood speeds drying. The target is under 20% moisture, which you can check with a moisture meter.
Does the type of wood matter?
Yes. Denser woods hold more heat per cord than lighter ones, and the University of Kentucky notes that density matters more than whether a tree is a hardwood or a softwood.
Should I harvest all the firewood my land can produce?
Generally, no. Forest management involves more than maximizing firewood. Harvesting affects wildlife habitat and future growth, so your state forestry agency or Cooperative Extension office can give region-specific advice.
This calculator provides planning estimates only. Actual sustainable harvest depends on forest composition, growth rate and management goals. Consult a forester or your state or Cooperative Extension forestry program for a site-specific assessment.
