The Straight Answer: How to Calculate Log Volume in 3 Steps
When a neighbor asks me how to calculate log volume, I give them the practitioner’s version, not the forestry textbook. Grab a tape measure, find the small-end diameter inside the bark, and multiply by length using a trusted formula. For a quick cylindrical estimate of an 8-foot log with a 12-inch small end, that’s about 6.3 cubic feet of wood.
The field method boils down to three steps: measure the log length to the nearest inch, measure the diameter at the small end (inside bark), and apply a log rule or cylinder formula. If you’d rather skip the arithmetic, our Log Volume Calculator applies the same scaling logic instantly and shows which rule it used.
Most beginners assume you measure the fat butt end because it looks like the “main” size. In reality, nearly every forestry standard scales from the small end because it is the least distorted by root flare and butt swell. That single choice can change your volume by 10–20% on a typical 16-foot sawlog.
One more non-obvious point: diameter is almost always averaged from two perpendicular measurements on the same end. A log is rarely a perfect circle, so taking one caliper reading lies to you. I carry a cheap log caliper, but a flexible tape wrapped around the small end (girth) divided by π works too.
Why Log Volume Isn’t Just “Length × π × Radius²” (The Real-World Twist)
A cylinder formula gives a theoretical maximum that I once mistakenly quoted to a firewood buyer. He asked for 4 cords; my math said his pile held 5. When we actually burned it, the delivered cordwood measured closer to 3.2 cords because of bark, gaps, and taper. The gap between geometry and reality is the whole game in log scaling.
Logs are not uniform cylinders. They taper from butt to tip, they bend (sweep), and they carry bark that isn’t wood. The thing nobody tells you about backyard scaling is that every formula is an estimate calibrated to a specific end use, not a precise geometric measurement of solid matter.
According to the USDA Forest Service, standardized log rules like Doyle and Scribner were developed in the 1800s to estimate board footage from sawlogs, not to measure solid wood cubic volume. That heritage means trade numbers can differ wildly from cubic footage, and a “board foot” is strictly a lumber measure, not a chunk of tree.
Before you calculate, decide your goal: firewood warmth (cubic feet or cords), sawtimber output (board feet), or international trade (cubic metres). The formula changes with the goal, and so does the acceptable error margin.
A Worked Example: Cubic Feet in a Standard 8-Foot, 12-Inch Log
The “People Also Ask” box wants to know: how many cubic feet are in 1 log? Let’s take the classic example—an 8-foot log with a 12-inch diameter. If we treat it as a cylinder with radius 0.5 ft, volume = π × 0.5² × 8 = 6.28 cubic feet.
But that’s the gross solid volume. Using the small-end rule (diameter taken inside bark at the 8-ft end), a 12-inch small-end log scales to roughly 5.9 cubic feet after accounting for ½-inch bark and slight taper. If you apply the Doyle rule, you get about 40 board feet, which converts to roughly 3.3 cubic feet of actual lumber—a huge difference.
The key insight: “1 log” is meaningless without diameter, length, and rule. A standard 8-ft, 12-inch sawlog is about 6.3 cubic feet of wood fiber, but only ~3.3 cubic feet of finished boards. When I quote volumes to landowners, I always state which number I mean.
For shipping or containerised trade, you’ll need cubic metres. Our CBM Volume Calculator converts that 6.3 cubic feet to 0.178 m³ in one click, saving you from manual division by 35.3147.
Common Log Volume Formulas Compared (and When to Use Each)
Below is the comparison table I wish I had when I started. It maps each formula to a real use case, not just its math. Notice that output units vary—some give cubic feet, others board feet or hoppus feet. This is the decision matrix that separates a confident landowner from someone guessing with a smartphone app.
| Formula | Inputs | Output | Best For | Major Caveat |
|---|---|---|---|---|
| Small-End Cylinder | Length, small-end diameter (inside bark) | Cubic feet (or m³) | Firewood, quick landowner estimates | Over-estimates by 5–15% due to taper |
| Doyle Rule | Length (ft), small-end diameter (in) | Board feet | Sawtimber in Eastern US, antique mills | Heavy underscaling on small logs (<20 in) |
| Scribner Rule | Length (ft), small-end diameter (in) | Board feet (log scale) | Western US timber sales, board trading | Assumes ¼-in kerf, loses accuracy on big diameters |
| JAS (Japanese Agri Std) | Length (m), top diameter (cm) | Cubic metres | Export logs to Japan, Pacific Rim | Uses top (small) end only, ignores butt |
| Hoppus Formula | Length (ft), girth (in) at mid | Hoppus cubic feet (≈0.785 of solid) | Tropical hardwood, imperial tonnage | Multiply by 0.785 to get true cubic feet |
The table is a decision matrix, not just trivia. If you’re a landowner selling a few walnut trees, Doyle may shortchange you on small stems; Scribner or a cylinder method is fairer. For a firewood buyer, cubic feet from small-end diameter is all you need.
The Small-End Cylinder Method (Firewood & Quick Estimates)
This is the “log volume 101” baseline. Formula: V = π × (D/24)² × L where D is inches, L is feet, result in cubic feet. I use it to estimate how many evenings a pile will heat my shop. It’s transparent and reversible—you can solve for length if you need a target volume.
The limitation is taper. A 16-foot oak with 18-inch butt and 12-inch top has about 9% more wood than the small-end cylinder predicts. For stacking firewood, that error is acceptable; for billing a mill, it isn’t.
Doyle Rule (Sawtimber in Eastern US)
Doyle is V = (D−4)² × L / 16 (board feet). The “−4” deducts for slab and saw kerf. The thing nobody tells you: on a 10-inch log it yields almost zero, which is why modern scalers avoid it for small timber. I once watched a buyer reject a load of 14-inch cherry because Doyle made it look thin; Scribner showed 30% more board feet.
Scribner Rule (Board Feet Trade)
Scribner uses a diagrammed log with ¼-inch kerf. It’s closer to real lumber on medium logs but still underestimates huge diameters. For a 24-inch × 16-foot log, Scribner gives ~260 bd ft; actual cleared lumber might be 300. It remains the law in many state timber sales, so check local statute before arguing.
JAS and Hoppus for Global Trade
JAS measures the top end in centimetres and length in metres, producing cubic metres. Hoppus, common in Myanmar or Ghana, uses girth at mid-length and outputs “hoppus feet”—a weird unit that is 78.5% of solid volume. If a contract says “HK” (Hoppus cubic feet), multiply by 0.785 to get real cubic feet. Miss that and you overpay by 27%.
Converting Between Cubic Feet, Board Feet, and Cubic Metres
Conversions are where beginners trip. One board foot is 144 cubic inches, or 1/12 of a cubic foot. So 12 board feet = 1 cubic foot of lumber, but not of log. A log’s “board foot scale” already includes milling waste, so you cannot reverse it to cubic feet of wood without knowing recovery rate (typically 40–60%).
For cubic metres, 1 m³ = 35.3147 cubic feet. I keep that constant taped to my scaling stick. When a German buyer asks for “Festmeter” (solid metre), they mean the cylinder volume; “Ster” is stacked firewood with air gaps—about 0.7 Festmeter per Ster.
If you regularly jump between systems, the CBM Volume Calculator on our site handles m³ ↔ ft³, but it won’t apply Doyle deductions. That’s why understanding the rule behind the number matters more than the calculator.
Remember: converting a Doyle board-foot number to cubic feet by dividing by 12 is wrong. You must first accept the rule’s built-in loss. I’ve seen inflated freight quotes from that exact mistake. For example, 1,000 Doyle board feet from a 14-inch log equals about 83 ft³ of lumber scale, but the actual solid wood was closer to 140 ft³—a 40% gap that wrecks a shipping budget.
Measuring Irregular and Bark-On Logs: What Nobody Tells You
The biggest gap in competitor articles is real-world messiness. Not every log is straight. When I scale storm-damaged timber, I face sweep (side bend), crook (end-to-end twist), and rot. Here’s how experience handles it with tools like a Haglöf caliper and a Suunto clinometer for slope length.
Dealing With Sweep, Taper, and Crook
For a swept log, measure diameter at the small end as usual, but if the mid-length diameter is more than 2 inches larger, some scalers use the average of small and large ends. The cylinder formula with average diameter corrects taper better: V = π × ((Dsmall+Dlarge)/48)² × L. I use this for bent maple because small-end alone undercounts by 8%.
Crook means the ends don’t align; you measure length along the centreline, not straight-line distance. Underestimating length by following the chord instead of the arc can short you 3–5% on a 20-footer. On a steep hillside, I clip a line to each end and read the slope distance, then convert to horizontal only if the contract demands it.
Bark Inclusion and Rot: Deductions
Bark-on logs need “inside bark” diameter. Use a bark gauge or knock off a chip. On thick-barked oak, bark can be ¾ inch per side—that’s 1.5 inches off diameter, costing 20% volume. Rot or hollow centres require deduction: if a 16-inch log has a 4-inch punky core, subtract area proportionally (1−(4/16)² = 93.75% sound).
The most people don’t realize: many states require scaling dry, bark-on, but trade contracts often say “dressed” or “bark-free.” Always read the contract’s defect deduction schedule before measuring. I lost a dispute once because I scaled bark-on while the mill’s policy deducted 10% for “natural bark variance.”
Visual Guide: Exact Measurement Points on a Log (Infographic)
Because words fail on curved wood, here’s a simple infographic I drew for my workshop wall. It shows where to put the tape. Use the small end (arrow A), take two perpendicular diameters (A1, A2), measure length along the grain (B), and mark defect (C).
Print that mental picture. When a log is leaning in a skid, you’ll still know which end is “small” and where to subtract rot. The red dots mark the two perpendicular caliper touches that average into your diameter.
Putting It to Practice: A Landowner’s Story
Two winters ago, a retired teacher called me to value a fallen ash. He’d been quoted $120 per “thousand board feet” using Doyle. I measured: 14-inch small end, 18-inch butt, 12 feet long. Doyle gave 84 bd ft (~7 ft³ lumber). Scribner gave 110 bd ft. Cylinder gave 9.8 ft³ solid.
I showed him the comparison table and explained the buyer’s rule shortchanged small logs. He negotiated on cubic feet of firewood instead (about 0.28 cord) and got a better deal. That story is why I preach: know your formula, know your use, and never accept a single number without the rule name.
The lesson extended to me: I’d once trusted a phone app that used Hoppus without labeling it. My export quote was 27% high. Now I always ask “which rule?” before I trust a volume. Experience is just corrected mistakes worn as badges.
Final Checklist Before You Scale That Pile
- Identify purpose: firewood (ft³), lumber (bd ft), or export (m³).
- Measure small-end diameter inside bark, two perpendicular reads averaged.
- Measure length along centreline, not straight chord.
- Apply the matching rule from the table; note its name on your sheet.
- Deduct visible rot, hollow, or excessive sweep per contract.
- Convert units carefully—never divide board feet by 12 to get log cubic feet.
- Cross-check with our Log Volume Calculator for sanity.
Follow that and you’ll calculate log volume with the confidence of someone who’s actually stood in the woods with a tape and a questionable quote. The math is simple; the judgment is earned after a few surprises.