Stacked wood and weight: from Rm to Fm and tonnes

Industrial and energy wood, and a good deal of short wood, is not measured log by log. It is stacked, weighed or both. This lesson shows how a stacked cubic metre becomes a solid cubic metre, how a tonne becomes a volume, and why a flat conversion factor and a factor built from the real stack behave differently.

German factors: flat averages

The RVR (Germany, Europe, 5th edition 2023) gives average factors from stacked cubic metres with bark (Rm m.R.) to solid cubic metres without bark (Fm o.R.): 0.70 for 1 m lengths, 0.65 for 2 m and 0.60 for 3 m. Longer pieces stack with larger gaps, so the factor falls.

For weight, 1 tonne oven-dry (atro) with bark equals a number of Fm o.R.: 2.2 for spruce and fir, 2.1 for pine and Douglas fir, 1.8 for larch, 1.5 for beech and 1.4 for oak. The heavier the species, the fewer cubic metres in a tonne.

Worked example. A delivery of 120 Rm of beech cut to 3 m. Solid volume: 120 x 0.60 = 72 Fm o.R. Oven-dry weight: 72 / 1.5 = 48 t atro. If the same 120 Rm were 1 m lengths, the solid volume would be 120 x 0.70 = 84 Fm o.R. and the weight 84 / 1.5 = 56 t atro (own calculation). Another check: 100 Rm of 1 m spruce is about 70 Fm o.R., and 10 Fm o.R. of spruce is 10 / 2.2 = 4.55 t atro.

The brochure states that these are averages for internal and statistical use and must not serve as a sales measure. For billing, the RVR describes the oven-dry tonne for industrial and energy wood: oven-drying per DIN 52 183 on at least 100 g weighed to 0.1 g, scale accuracy 20 kg, range 50 t, and weighing slips to the forest owner within 14 days. For stem wood the commercial basis remains volume.

Sweden: a factor built from the real stack

The Biometria stack regulation (Sweden, Europe, version of 1 January 2026) measures volume in m3sub, intended to match top-butt log measurement. The stack volume is the product of the external dimensions multiplied by a wood-volume percentage.

The regulation's own example: 6.00 x 3.01 x 1.08 = 19.505 m3t (external volume). At 55% this gives 10.73 m3sub. Base percentages are 70% for spruce, 68% for pine, 66% for aspen, 65% for alder and oak, and 64% for birch, beech and ash. They are then adjusted for bark, stacking, crookedness, snow and ice, logging waste, wood length and stack height. At storage sites the stack height must be 100 to 300 cm, with at least 1 m between stacks.

Worked example. A pine stack measures 5.40 x 3.10 x 1.05 m. External volume: 17.58 m3t. At the 68% base percentage: 11.95 m3sub. If the measurer's adjustments (snow, crooked wood) lowered the percentage to an invented 59%, the volume would be 10.37 m3sub, a difference of 1.58 m3 on one stack (own calculation; the adjustment tables are not in the portal's articles, so 59% is for practice only).

What the contrast teaches

A flat factor (Germany) gives the same Fm for a tidy stack and a crooked, snowy one. The Swedish approach lets snow, ice and poor stacking visibly change the payment. Do not use one country's factor for the other's wood, and do not use an average for a delivery whose stacking you know to be unusual.

Weight, moisture and transport

The Forest Products Laboratory green-density tables could not be opened for the portal's logistics article, so no green weight values are quoted. A mill that buys by weight should sample its own tonne-to-cubic-metre relationship by species and season, since water content changes the weight of a cubic metre. The FVA warns that sales lots can be mixed during transport, so lot marking and delivery slips are the base of traceability.

Key points

• RVR (Germany) stack factors: 0.70 (1 m), 0.65 (2 m), 0.60 (3 m) from Rm m.R. to Fm o.R.; they are averages and not a sales measure.
• 120 Rm of 3 m beech is 72 Fm o.R. and 48 t atro; as 1 m lengths it would be 84 Fm o.R. (own calculation).
• The Swedish stack volume is length x width x height x a wood-volume percentage (the regulation's example gives 10.73 m3sub at 55%).
• A flat factor hides snow and poor stacking; a built-up factor shows them but needs a competent measurer.
• Weight-based buying needs the mill's own tonne-to-cubic-metre data and a clear statement of oven-dry or delivered tonnes.