Log weight calculator
A 12 inch log 8 feet long at 40 pounds per cubic foot weighs well over 100 kg, and the result gives the exact pounds and kilograms. Enter the species density, diameter and length before you load a trailer or call a crane. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Density
- 40
- Diameter
- 12
- Length
- 8
- Volume ft3
- 6.2831853072
- Weight lb
- 251.3274122872
- Weight (kg)
- 114.0001965853
A round timber log is bought, sold, and hauled by mass, not by a sawn board-foot tally. Foresters, firewood yards, mill buyers, crane operators, and anyone loading a trailer need the weight of a log from three numbers they already have: the bulk density of the species, the diameter they can tape, and the length they can measure. This log weight calculator treats the stem as a right circular cylinder, multiplies that solid cubic volume by species density, and returns the mass in both pounds and kilograms. Diameter is in inches, length is in feet, and density is in pounds per cubic foot of the wood as it actually sits—green, air-dry, or kiln-dry, whichever handbook table you are using.
How cylindrical log volume becomes pounds and kilograms
A timber log is modelled as a right circular cylinder whose axis is the stem. Volume in cubic feet is π times the square of the radius in feet times the length in feet, which is the same identity as π d² L / 4 when diameter and length share a unit. Because field crews tape diameter in inches and length in feet, the radius in feet is diameter divided by twenty-four: half of the inch diameter, then divided by twelve inches per foot.
Species density is pounds per cubic foot of the wood in the moisture condition you care about, so weight in pounds is that cylindrical volume times density. Kilograms follow from the exact avoirdupois factor 0.45359237 kilograms per pound.
Passing density as a number rather than hiding a species table inside the solver is deliberate: green white oak can sit near fifty-five to sixty pounds per cubic foot, green eastern white pine nearer twenty-five to thirty-five, and kiln-dry stock of the same species is substantially lighter because water has left the cell cavities. A page that silently assumed oak would lie for pine, and a page that assumed oven-dry specific gravity would understate a green log on a truck.
The cylinder is the contract this landing serves; it is Huber's mid-diameter solid when you tape at mid-length, not Smalian's two-end frustum, not Newton's three-diameter formula, and not a Doyle or Scribner board-foot rule. The calculator does not subtract bark, heart rot, or a hollow, and it does not add a moisture or packing allowance; those are job-specific factors applied after the solid take-off so a quote stays transparent.
Diameter and length must be strictly positive finite numbers: a zero or negative diameter cannot be a stem, and a zero or negative length cannot be a log.
What you send, which units to use, and how validation fails
Convert millimetres of diameter to inches by dividing by 25.4 before you call; convert metres of length to feet by multiplying by 3.280839895; convert kilograms per cubic metre to pounds per cubic foot by multiplying by 0.06242796. Mixing centimetres of diameter with a density of 0.55 specific gravity without converting would understate mass by orders of magnitude, so the contract keeps one inch-foot-pound set and leaves conversion to the caller.
A twelve-inch by eight-foot log at forty pounds per cubic foot yields two-π cubic feet, eighty-π pounds, and the matching kilogram figure. Validation failures name the offending field so a form can highlight diameter when someone types zero, or length when a spreadsheet leaked a negative. Upper and lower limits keep intermediate products finite: each field must be at least 1e-15 and at most 1e12.
Where a log weight calculator earns its keep
Firewood yards and campground suppliers estimate green or seasoned mass before they load a pickup so they can quote a stem by the pound instead of guessing from a photo of a pile. Logging contractors and mill intake desks need a pound and kilogram figure that matches the public calculator when a scaler pastes diameter, length, and a species density from the handbook.
Trucking and crane teams convert those masses into axle load and lift plan numbers, which is a different search from dimensional billable-weight factors and belongs on this landing because the question is the timber mass itself. Educators teaching density as mass over volume, and forestry students comparing a cylinder take-off with a Smalian frustum, all want the same three-input contract. Curriculum authors can pin goldens: twelve inches by eight feet at forty pounds per cubic foot must stay eighty-π pounds after the documented rounding.
If you later need Doyle board feet, Scribner volume, a two-end Smalian frustum, bark allowance, or a species lookup table as a first-class form, treat those as separate search intents rather than overloading this log-weight page. The tool is a solid cylindrical take-off, not a substitute for a truck scale, a mill ticket, or a green-weight table that already folds in moisture.
What you can do with it
Quote firewood stems by the pound
Yards enter species density, diameter, and length to price a round log before splitting, so the mass on the ticket matches the public calculator in pounds and kilograms.
Logging truck and mill intake mass
Scalers and haulers convert a taped cylinder into pounds and kilograms for axle load, mill receipts, and crane lift plans without opening a CAD mass-properties panel.
Classroom cylinder density checks on timber samples
Teachers and LMS auto-graders verify that π r² L times a handbook lb/ft³ density yields the expected pound and kilogram mass for a measured round sample.
FAQ
How is the weight of a log calculated from density, diameter, and length?
The stem is treated as a right circular cylinder. Weight in pounds is that volume times species density in lb/ft³; kilograms are pounds × 0.45359237.
What species density should I use for a timber log?
Use the handbook bulk density for the species and moisture you actually have. Green pine often sits near 30–40 lb/ft³; green oak nearer 45–60. Kiln-dry stock of the same species is lighter. Density is a required input so the solver does not guess the grade.
What happens if diameter or length is zero or negative?
Diameter and length must both be positive; a zero or negative size cannot be a physical log and is not billed.
Are diameter and length in inches, feet, or metres?
Diameter is inches; length is feet; density is lb/ft³. Divide millimetres by 25.4 for diameter, multiply metres by 3.280839895 for length, and multiply kg/m³ by 0.06242796 for density. Mixing units without converting understates the mass.
Does the log weight account for bark, rot or a hollow?
No. The log is treated as a solid cylinder of wood. Subtract bark, heart rot or a hollow yourself, and add any moisture allowance afterwards, so the figure you quote stays clear.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/build/log-weight \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"density":40,"diameter":12,"length":8}'const res = await fetch("https://api.kit.forhosting.com/build/log-weight", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"density": 40,
"diameter": 12,
"length": 8
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/build/log-weight",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"density": 40,
"diameter": 12,
"length": 8
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/build/log-weight", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"density":40,"diameter":12,"length":8}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"density":40,"diameter":12,"length":8}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/build/log-weight", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"density": 40,
"diameter": 12,
"length": 8
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "build.log_weight",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_dim | 1000000000000 |
min_dim | 1e-15 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
A diameter or length that is zero or negative cannot be a physical log: the task fails with invalid_input and is not billed.
How cylindrical log volume becomes pounds and kilograms
The same three inputs always produce the same volume and the same two masses after fixed twelve-decimal rounding, so goldens, widgets, and API clients never disagree on an eight-foot twelve-inch log at forty pounds per cubic foot.
What you send, which units to use, and how validation fails
Send three required numeric fields. density is a finite positive number for species bulk density in pounds per cubic foot; aliases rho, species_density, and density_lb_ft3 are recognized so a handbook column can be pasted without a rename. diameter is a finite positive number for the log diameter in inches; aliases D, d, and dia are accepted so a cut list does not need a rename. length is a finite positive number for the log length in feet; aliases L, l, and len are recognized. Strings that parse as finite numbers are accepted the same as JSON numbers. On success the response echoes the cleaned inputs, publishes volume_ft3 as π times (diameter over 24) squared times length, weight_lb as that volume times density, weight_kg as weight_lb times 0.45359237, and formula as the cylindrical identity. A non-positive diameter or length is the highlighted contract failure: the task returns invalid_input and does not consume prepaid balance. Successful API calls use the published base of $0.002 per item.
Where a log weight calculator earns its keep
Failed validation is not billed; only a successful pound and kilogram figure consumes the published $0.002 base.
Technical questions
What does the log weight calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.