How round log volume is measured
Sawn timber is measured by length × width × thickness, but a round log has no width or thickness — only a girth (the distance around it) and a length. Timber traders in India, Pakistan, Bangladesh, Africa and the UK have used the Hoppus or quarter-girth formula for centuries to turn those two measurements into cubic feet (CFT).
This calculator gives you both the Hoppus volume (what most buyers and sellers use) and the true geometric volume, so you always know which number you are looking at.
How to use the calculator
- Choose Hoppus (trade standard) or True volume.
- Choose whether you measured the girth (with a tape around the log) or the diameter.
- Enter the girth in inches (or cm, feet, metres) and the length in feet (or metres), plus how many logs of that size.
- Add a row for each different log size. Enter a bark allowance and a rate per CFT if you need them.
Round log CFT formulas
Hoppus CFT = (Girth in inches ÷ 4)² × Length in feet ÷ 144 True CFT = Girth² × Length ÷ (4 × π) (girth and length in feet) Girth = π × Diameter
The Hoppus result is always π ÷ 4 ≈ 78.5% of the true volume. Put the other way round, one Hoppus cubic foot equals 1.273 true cubic feet. The “missing” 21.5% roughly matches the wood lost when a round log is squared into beams and planks, which is why the trade prefers it.
Worked example
A teak log has a mid-girth of 60 inches and a length of 10 feet:
- Quarter girth = 60 ÷ 4 = 15 inches
- Hoppus CFT = 15² × 10 ÷ 144 = 225 × 10 ÷ 144 = 15.625 CFT
- True volume = 15.625 × 1.273 ≈ 19.89 CFT
At ₹1,200 per CFT (Hoppus), that log costs 15.625 × 1,200 = ₹18,750.
Hoppus CFT table (per 10 ft length)
| Mid-girth | Hoppus CFT (10 ft) | True CFT (10 ft) |
|---|---|---|
| 24 in (2 ft) | 2.500 | 3.183 |
| 36 in (3 ft) | 5.625 | 7.162 |
| 48 in (4 ft) | 10.000 | 12.732 |
| 60 in (5 ft) | 15.625 | 19.894 |
| 72 in (6 ft) | 22.500 | 28.648 |
| 84 in (7 ft) | 30.625 | 38.993 |
For other lengths, scale in proportion: a 15 ft log has 1.5 times the CFT shown.
Tips for measuring logs
- Measure girth at mid-length. Logs taper from butt to top; the middle gives a fair average.
- Keep the tape square to the log, not at an angle, or the girth reads too large.
- Round down to the nearest inch if that is your local practice — many markets do.
- Agree the method and bark allowance before you agree a price. The difference between Hoppus and true volume is more than 27%.
- In metric: enter girth in centimetres and length in metres; the calculator still returns CFT and cubic metres.