Log Weight Calculator — By Species and Size
A log’s weight is the first fact of every job it starts — the trailer’s limit, the mill’s handling, the firewood season’s planning all hang on it. Enter the log’s length and both end diameters, choose the species, and this calculator returns the green weight by the forester’s own volume formula, in pounds and kilos.
Smalian's Formula: The Forester's Honest Compromise
A log is a tapered cylinder, and forestry prices it with Smalian's formula: volume = the average of the two end areas × length. It is not the exact volume of a cone frustum (Newton's formula, which samples the middle too, is closer), but it is the standard of log rules and trade practice — computable from two tape measurements at the log's ends, honest within a few percent on sound logs, and the same from Maine to Oregon, which matters more to a market than the last decimal. The ends enter as inside-bark diameters (the wood, not the wrapper — bark's own few percent is handled in the calculator's note), squared through π into areas, averaged, and multiplied by length. Weight is then one more multiplication, by the species' green density — and "green" is the operative word, since a fresh log is substantially water wearing a wood costume.
Worked Example: A 16-Foot Red Oak
The defaults weigh a sawlog of the classic American hardwood: 16 feet long, 20 inches at the butt, 16 at the small end, red oak at 64 lb/cu ft. End areas: the butt, π × (10/12)² ≈ 2.18 sq ft; the top, π × (8/12)² ≈ 1.40 sq ft; average 1.79 sq ft. Volume: 1.79 × 16 ≈ 28.6 cu ft. Weight: 28.6 × 64 ≈ 1,830 lb. In round terms, a hair under a ton: a weight that a half-ton truck should not carry, a one-ton handles singly, and a firewood splitter's season plans around precisely. Species is destiny in this arithmetic — the identical log in white pine (36 lb/cu ft) weighs about 1,030 lb, in hickory (66) about 1,890 — which is why the selector, not the tape, carries the estimate's largest uncertainty after moisture itself.
Green Weight, Dry Weight and the Water Between Them
A freshly felled hardwood holds water equal to a large fraction of its dry mass — green densities in the selector run roughly 1.5–1.8 times the wood's kiln-dry density — and it sheds that water at its own pace: end grain first, a season for firewood splits, years for a beam. Every downstream use prices a different point on that drying curve: the sawmill weighs green (its log yard scales by the ton), the firewood seller delivers "seasoned" (a claim about months, audited by the moisture meter), and the timber framer times joinery to the log's movement. The calculator's green figure is therefore the starting weight, the note's 15–25% seasonal loss is the trajectory, and any single number quoted without its moisture state is a rumour. For hauling decisions — the use where error bites — take the green figure and round up, exactly as the note instructs: nobody's trailer ever failed from a log that weighed less than feared, and several have from the other direction.
Hauling: Where the Estimate Meets the Law
The calculator's figure becomes legal arithmetic at the trailer: axles and gross vehicle ratings are enforced numbers, and a load plan built on a flattering log weight is a fine with a story attached. The prudent loading method weighs the arithmetic twice — sum the calculator's green estimates, round the total up by the note's margin, and compare against the lower of the trailer's rated payload and the tow vehicle's remaining capacity after fuel and passengers; then split loads by the scale's answer, not by optimism, when the sums approach the line. Log length is the smuggler's variable in these calculations — an extra two feet of butt log on a tapered stem adds weight at the fat end's rate, which the two-diameter formula prices correctly and a single-diameter guess never does. Measure both ends, every time: Smalian's discipline is the overload ticket's only reliable defence on the road.
The Doyle Rule's Warning, Printed on a Weight Page
Log buyers meet weight through the rules that price lumber yield, and one of them deserves its warning label here because generations of small woodlot owners were underpaid by it: the Doyle rule, still legal tender in some markets, scales a 16-inch, 16-foot log at about 96 board feet where the International rule gives about 160 — Doyle's formula ((D−4)/4)² × L punishes small logs savagely and barely improves with size. A seller armed with this page's weight (mass is rule-proof) and the International figure for the same log negotiates with physics rather than with a 19th-century formula's thumb on the scale. Know which rule a mill buys by before the truck rolls; the calculator's species densities are the same in every market, but the rules' generosity is not, and the difference on a truckload is a winter's firewood money.
Related Tools
More from the Construction Calculators hub: the Lumber Weight Calculator for the same wood after the mill, and the Tree Diameter Calculator for measuring this log while it was still standing.
Frequently Asked Questions
How accurate is this estimate, honestly?
Within roughly ±10% for sound, straight logs measured inside bark — the compounding of Smalian's small geometric optimism, species density variation within a species (site and tree move it by several percent), and moisture's mood. That precision plans trailers, skidders and firewood racks perfectly well. Where money changes hands by the ton, the scale at the mill is the arbiter and this page is the estimate that tells you whether the scale's story is plausible — the same audit relationship every calculator on this site maintains with the official instrument of its trade.
Why measure inside the bark, always?
Because the wood is the cargo and the bark is packing material: log rules, mill scales and density tables are all built on the wood's dimensions, and a 20-inch oak carries roughly an inch of bark diameter that is not oak. If your tape only has the outside measurement, subtract about twice the bark thickness (commonly ½–1 inch of diameter on mature hardwoods, less on pines) before entering. The calculator's note already forgives a few percent for bark if you forget — but the inside measurement is the professional habit, taken at the log's cut faces where the bark line is printed for all to see.
What is a cord of firewood in these terms, then?
A cord is a volume (128 cu ft of stacked wood, roughly 80–90 cu ft of solid wood within it), and its weight is this calculator's arithmetic at pile scale: green red oak runs about 5,000–5,500 lb per cord, white pine about 3,600–4,000 — which is why the same "truckload" is one cord of pine and two-thirds of a cord of oak, and why firewood sold by weight is the honest market's preference. Seasoning drops the oak cord toward 4,000 lb as its water leaves — the drying curve of the previous section, invoiced.
How does log weight relate to board feet and lumber yield, then?
Loosely and famously contentiously: log rules (Doyle, Scribner, International) estimate the lumber a log will yield, and the International quarter-inch rule is the honest broker among them — a 16-foot, 16-inch-small-end log scales about 160 board feet by it. Weight is the blunter instrument this page plays: it prices the log as mass for hauling and handling, while the rules price it as future lumber for buying and selling. The two meet at the mill gate, where the same log is weighed, scaled, and argued about in both currencies.
Can I weigh a log still standing in the tree?
In the forester's sense, yes — the standing-tree version of this arithmetic estimates the stem's volume from diameter at breast height and height (the tree-diameter page on this site begins that work), then applies the same densities. Felling plans, crane picks for urban removals and timber cruises all run on such estimates, with wider error bars for the crown's branches (add a fifth to a third for full-canopy hardwoods when the whole tree must move). The calculator's two-end formula takes over the moment the saw makes the ends available to measure, which is the usual order of operations in any case, on any landing, in any season.
Why do two logs of the same species differ, then?
Site, age and the tree's own history: fast-grown plantation wood of a species runs lighter than old-growth of the same name (wider rings, more earlywood), heartwood and sapwood differ in moisture, and a log from a wet bottomland carries more water than its ridgetop brother. The selector's single figure per species is the published typical — the professional response to the spread is not a better table but the note's rounding discipline: plan equipment and trailers from the top of the plausible range, and let the log surprise you pleasantly, at 1,700 lb instead of its feared 1,900.