Why small-end diameter matters
Sawmill recovery is set at the small end. A 4-metre log with 25 cm SED yields the same clear lumber from end to end; a 4-metre log with 18 cm SED at one end and 35 cm at the other behaves like an 18 cm log throughout the breakdown. Specifying logs by SED band guarantees a predictable mill yield.
Standard SED classes
14-19 cm: small sawlogs, pulpwood, packaging timber and chip feed. 20-29 cm: general sawmill workhorse band, framing, scantlings, pallet stock. 30-39 cm: structural and joinery production, predictable yield, balanced economics. 40+ cm: peeler logs, premium clears, large-section joinery, beam-grade sawlogs.
NZ export contracts often define narrower bands inside these (e.g. 28-32 cm SED for precision sawmill programmes).
Standard lengths
2.4 m: short sawlog programmes, packaging and pallet stock. 3.0 m, 3.6 m: pallet and packaging sawmills. 4.0 m, 5.0 m: standard structural sawmill workhorse lengths. 6.0 m+: long structural and engineered wood applications (LVL billets, dimensional framing).
Most contracts allow ±5 cm tolerance on length; the mill cuts to multiples of the buyer's preferred dimensional length.
Volume calculation: JAS-m³ and the Smalian formula
Two methods dominate. JAS-m³ (Japanese Agricultural Standard, used by NZ exporters): volume = SED² × length × π / 40,000, effectively the cylinder volume at the small end. Smalian's formula: V = (Asmall + Alarge) / 2 × L, averages cross-sectional area at both ends.
JAS-m³ is conservative (underestimates volume) but standard for NZ export contracts. Smalian is fairer but slower to apply consistently. Always confirm which method the contract uses before agreeing to a volume specification.