Beispieldaten-Modus. Die gezeigten Beispielfirmen, Angebote und Anfragen sind fiktiv (KI-Bilder) und zählen nicht in die Statistik unten.
Lesson 2 of 7
Recovery, conversion factors and value recovery
Recovery is the headline productivity KPI of a sawmill, and also the most misused. A mill that turns more of each log into saleable boards earns more from the same wood supply. But published recovery numbers are only comparable if their definitions match.
Definitions
Volume yield (volume recovery) is sawn volume divided by log volume:
volume yield (%) = sawn volume (m³) / log volume (m³) × 100
Three choices change the result without any change in mill performance:
- State of the lumber: rough green, kiln-dried or planed. Drying shrinks the wood and planing removes material.
- Log measurement: over or under bark, mid-diameter formula or scanner.
- What counts as product: main product only, or everything sold as lumber.
The inverse is the conversion factor, cubic metres of roundwood per cubic metre of sawnwood: recovery = 1 / conversion factor.
In North America, lumber recovery factor (LRF) is board feet of lumber per cubic foot of log, and cubic lumber recovery (CLR) is the cubic volume ratio. LRF is not a percentage and cannot be compared with a European volume yield.
Value recovery (value yield) is total sales value of all products, including residues, per cubic metre of log, or per euro of log cost:
value yield = (lumber revenue + by-product revenue) / log volume
A mill with lower volume recovery but a better grade and size mix can have the higher value recovery.
Reference figures and how to read them
An FAO, ITTO and UNECE illustration for construction softwood shows how the state of the lumber changes the answer: rough green 1.57 m³ of roundwood per m³ sawnwood (64% recovery), rough dry 1.63 (62%), shipped 2.08 (48%). It is an illustration, not country data.
The same publication's national conversion factors are 1.59 for coniferous sawnwood in Germany (Europe) and 2.04 for the United States (North America). The basis (log measurement, lumber state) of each was not verified, so the gap is not a performance ranking.
Worked example: from conversion factor to recovery
Germany: 1 / 1.59 = 0.629, about 63%. United States: 1 / 2.04 = 0.490, about 49%. The 14-point gap may come purely from measurement conventions, so it must not be read as "German mills are better".
What moves recovery
The USDA review by Steele (1984, North America; old, indicative only) lists log diameter, taper, kerf, sawing variation, product mix, operator decisions, equipment condition and sawing method. Documented effects:
| Factor | Reported effect | Region and source |
|---|---|---|
| Small logs | Planed-board yield 43.7% for all logs but 35.8% for logs under 185 mm top diameter (simulation) | Sweden, spruce and pine, Fredriksson 2015 |
| Taper | Main-product yield falls from 49% to 35% as taper rises from 5 to 25 mm over the log (same lamella 43 × 146 × 4,000 mm) | Austria, Blinzer and Treml 2022 |
| Kerf | 12/32 to 9/32 inch raised board-foot yield by 7% for small logs | USA, Steele 1984 |
| Sawing variation | About 2.5% more recovery for each 0.030 inch removed from product thickness | Alaska, Kilborn 2002 |
Kerf savings are discontinuous: they appear when a thinner saw tips the log into a better sawing pattern. Thinner saws also need good guiding, or variation rises and the gain is lost.
Worked example: oversizing
Using the Kilborn rule of thumb, removing 0.060 inch of oversizing gives roughly 2 × 2.5% = 5% more recovery. This is an estimate from Alaskan mills; a modern European high-speed line may differ, and no open European measurement was found to compare.
Checklist: defining a recovery KPI in your own mill
- Fix the log basis (over or under bark, how diameter is measured).
- State whether lumber is counted green, dried or planed.
- Record log size class, species and product mix next to every yield figure.
- Report volume and value together, with price basis and date.
- Repeat the same procedure every quarter, so you benchmark against your own history first.
Key points
recovery = 1 / conversion factor; 1.59 gives about 63% and 2.04 about 49%, but the bases are unverified, so no ranking follows.- Volume yield depends on lumber state and log measurement; always define both before comparing.
- Value recovery combines yield, grade, size mix and residues; it can rise while volume recovery falls.
- Small logs, taper and sawing variation measurably reduce recovery (regional figures above).
- Kerf and oversizing gains are real but depend on pattern changes and good guiding.