Buying logs: measuring volume and grading quality

A sawmill does not simply buy "logs". It buys a volume, a quality, a delivery date and a risk profile, and each is fixed by a measurement rule, a grading rule and a contract clause. This lesson covers the first two.

Why measurement is a commercial question

Log volume is the basis of nearly every payment. Random measuring errors cancel out over large batches, but a systematic error never cancels. A caliper that reads one centimetre too high is a price change on the whole batch, which is why contracts name the rule, the rounding and the instrument calibration.

Europe: mid-diameter and the Huber formula (Germany)

The German framework agreement for round timber trade (RVR, 5th edition 2023) is a voluntary private agreement that applies only when buyer and seller include it in the contract. It measures the mid-diameter without bark, rounded down to whole centimetres, and computes volume as:

V = 0.7854 x d^2 x L / 10,000 (d in cm, L in m, result in m³ solid without bark)

Because volume is proportional to the square of the diameter, small diameter errors become large volume errors.

Worked example 1. A log with 30 cm mid-diameter and 5.00 m length: 0.7854 x 900 x 5 / 10,000 = 0.353 m³, reported as 0.35 m³.

Worked example 2. What if the diameter is read 1 cm too high, 31 cm instead of 30 cm? The volume error is (31^2 - 30^2) / 30^2 = 61 / 900 = about 6.8%.

The RVR also gives a length allowance of 1% of order length (minimum 10 cm, excluded from volume) and average stack factors, for example 0.70 for 1 m wood, which it states are for internal and statistical use, not a sales measure.

Sweden: stacks built from the real dimensions

The Swedish regulation (Biometria, stacks, version of 1 January 2026) calculates stack volume as the product of the external dimensions multiplied by a wood-volume percentage. The base percentages are 70% for spruce and 68% for pine, then adjusted for bark, stacking, crookedness, snow and ice and other factors. The regulation's own example is a stack of 6.00 x 3.01 x 1.08 = 19.505 m³t, which at 55% gives 10.73 m³sub. The contrast with the German flat factors is useful: the Swedish figure is built up from the actual stack.

North America: board-foot log rules

North American mills use rules that estimate sawn recovery from small-end diameter and length. For 16-foot logs (USDA NA-FR-15; the Scribner and Doyle columns are shown as printed, with unresolved scaling):

At 16 in., Doyle gives 144 / 180 = 80% of the International figure, which is 20% less. At 30 in. the rules converge. A price quoted per thousand board feet Scribner cannot be compared with a price per solid cubic metre without a size-dependent conversion agreed in writing.

Grading

Quality classes are the second half of the price. Visual grading of round timber follows the EN 1927 series (softwoods) and EN 1316 (hardwoods); the articles do not quote their paywalled limits, so name the exact part and edition in a contract. National frameworks use similar letter ladders that are not equivalent. The RVR uses A (excellent), B (normal), C (more or stronger defects) and D (usable but below C). The Polish State Forests technical conditions use a similar A-D ladder with quantified limits, for example sweep limits of 1 cm per metre for class A and 2, 3 and 5 for B, C and D in conifer long logs.

Checklist: what a log purchase contract should fix

• the measurement rule and its version
• place of measurement and who pays for it
• the grading standard, who grades, and the seller's right to witness
• allowances and rounding
• tolerance, delivery period and storage responsibility

Key points

• A systematic measuring error never cancels out; fix the rule, rounding and calibration in writing.
• Huber-type volume grows with the square of the diameter: a 1 cm error on a 30 cm log is about 6.8% of volume.
• Swedish stack volume is built from external dimensions times a wood-volume percentage; the German RVR stack factors are averages, not sales measures.
• North American log rules (Doyle, Scribner, International) disagree most on small logs; do not compare them with cubic prices without a written conversion.
• Letter grades from different countries are not equivalent.