Why log measurement is a payment question

A sawmill does not buy "logs". It buys a volume, a quality, a delivery date and a risk profile, and each is fixed by a rule: a measurement rule, a sorting rule, a storage condition and a contract clause. This course follows a log from the forest road to the saw line and shows where each rule turns wood into money. Every formula is worked with numbers.

Volume is the base of the payment

Log volume is the base of nearly every payment in the wood chain. A forest owner is paid per cubic metre, and the mill's yield statistics divide sawn volume by log volume. If the log volume is wrong, both are wrong at the same time.

The Swedish regulation on log volume under bark (Biometria, version of 1 April 2025, Europe) states the principle: systematic errors must be insignificant, and for batches over 10 m3 the permitted batch deviation decreases as batch size grows (the document does not print the values). This separates two kinds of error:

• Random errors (one log read a little high, the next a little low) cancel in a large batch.
• Systematic errors (a caliper that always reads high, a rounding rule that always goes one way) never cancel. They grow with the batch.

That is why billing rules fix rounding conventions and require calibrated instruments, and why a contract should name the measurement rule rather than just say "cubic metres".

Why diameter matters so much

Under the Huber-type formula of the German framework agreement (Germany, Europe), volume is proportional to the square of the mid-diameter. For a 30 cm log, a 1 cm error is (31 squared minus 30 squared) divided by 30 squared, or 6.78% of volume. On a 20 cm log the same centimetre is 10.25%, and on a 50 cm log it is 4.04% (own calculations). Thin logs suffer most in relative terms.

Worked example. A supplier delivers a batch whose true Huber volume is 1,200 m3. Every log has a true mid-diameter of 24 cm, but the caliper reads 25 cm. The volume is overstated by (625 minus 576) divided by 576, which is 8.51%, or about 102 m3. At an invented price of 85 per m3 the overpayment is about 8,700 on one batch (own calculation). Nobody cheated; one instrument was a centimetre off.

The same log has many "volumes"

Before comparing two numbers, ask which conventions each one uses:

1. Solid or stacked. Solid cubic metres (Festmeter, Fm) count wood only. Stacked cubic metres (Raummeter, Rm) include the air gaps.
2. Over or under bark. The German rule uses solid cubic metres without bark (Fm o.R.); stacked metres with bark are written Rm m.R.
3. Which formula. A mid-diameter formula, an end-area formula, or a scanner that adds up thin slices.
4. Which length. Order length, delivered length, or length less an allowance.
5. Which unit family. Cubic metres in Europe, board feet in much of North America.

Measurement rules change the denominator of every yield figure, so 50% from one study and 72% from another can both be correct and still not be comparable (portal yield article).

Rules are agreements, not laws of nature

The German statutory Forst-HKS lost validity on 31 December 2008. It was replaced by the voluntary "Rahmenvereinbarung fuer den Rohholzhandel in Deutschland" (RVR), signed on 11 December 2014 by the forestry and timber industry councils (DFWR, DHWR) and applied since 1 January 2015; the brochure used here refers to the 5th edition of 1 December 2023. It applies only when buyer and seller include it in the contract, in whole or in part. Austria follows Oe-NORM L1021 and the Holzhandelsusancen, Sweden has the Biometria regulations, and Poland's State Forests publish technical conditions. They resemble each other but are not interchangeable.

So the first line of any log purchase should name the rule and its edition. A price per cubic metre is meaningless until you know which cubic metre.

Where the course goes

Every lot raises four questions: how much (measurement rule), what kind (sorting and grading), when and in what state (storage), and whose cost (who measures and pays). The next lessons take these in turn: one log (lessons 2 and 3), piles and weights (4), North American log rules (5), sorting (6), money (7), storage and traceability (8).

Key points

• Log volume is the base of almost every payment in the wood chain, so a measurement error is a price error.
• Random errors cancel in large batches; systematic errors, such as a caliper that reads high, never do.
• Under a Huber-type formula volume goes with diameter squared: 1 cm is 6.78% on a 30 cm log and 10.25% on a 20 cm log (own calculation).
• A cubic metre can be solid or stacked, over or under bark, with different formulas and lengths; name the rule and its edition.
• The German RVR is voluntary and applies only if the contract says so.