Log CFT calculator
Girth and length in, CFT out — by the quarter-girth (Hoppus) method the timber trade uses.
Type in either box — the other one fills in.
| # | Girth | Length | Hollow | Logs | CFT | |
|---|---|---|---|---|---|---|
| Total | 0 | 0 | ||||
| Total in CBM | 0 | |||||
How the CFT of a log is calculated
The timber trade measures a round log by its girth — the tape goes round the middle of the log — and its length. The quarter-girth or Hoppus method treats the log as a square beam whose side is a quarter of the girth, so its volume is that square times the length:
CFT = (girth ÷ 4)² × length
With girth in inches and length in feet, that is:
CFT = girth × girth × length ÷ 2304
With girth in centimetres and length in metres:
CFT = (girth ÷ 400)² × length × 35.3147
Worked example. A log 12 metres long with a girth of 99 cm: 99 ÷ 400 = 0.2475; squared, 0.06126; times 12, 0.735 cubic metres; times 35.3147, 25.96 CFT.
The quarter-girth figure is about 78.5% of the log’s true round volume. That is deliberate: it allows for the bark and for the wood lost when the log is squared, and it is the figure most yards buy and sell by.
Hollow logs
A tape cannot go round a hollow, so the hollow is measured across, as a diameter. Its girth is π times that, and it comes off the log by the same quarter-girth rule, so a hollow log and a sound one are measured the same way:
hollow = (π × diameter ÷ 4)² × length
Sawn timber
CFT = length (ft) × width (in) × thickness (in) ÷ 144
A plank 12 ft long, 6 in wide and 2 in thick is exactly 1 CFT. In metric, length in metres × width in millimetres × thickness in millimetres ÷ 1,000,000 gives cubic metres; one cubic metre is 35.3147 CFT.
लकड़ी का CFT कैसे निकालें
गोल लट्ठे का CFT उसकी गोलाई (गर्थ) और लंबाई से निकाला जाता है: गोलाई को 4 से भाग दें, उसका वर्ग करें और लंबाई से गुणा करें। गोलाई इंच में और लंबाई फ़ुट में हो, तो CFT = गोलाई × गोलाई × लंबाई ÷ 2304। चिरी हुई लकड़ी का CFT = लंबाई (फ़ुट) × चौड़ाई (इंच) × मोटाई (इंच) ÷ 144। एक CBM में 35.3147 CFT होते हैं।
Questions
How do you calculate the CFT of a log?
Measure the girth (the distance round the log at its middle) and the length. Divide the girth by 4, square it and multiply by the length. With girth in inches and length in feet, CFT = girth × girth × length ÷ 2304. With girth in centimetres and length in metres, CFT = (girth ÷ 400)² × length × 35.3147.
What is the Hoppus or quarter-girth method?
The traditional way the timber trade measures round logs: the log is treated as a square beam whose side is a quarter of its girth. It gives about 78.5% of the true round volume, which allows for the bark and the waste of squaring the log, and it is the figure most yards in India buy and sell by.
How do I deduct a hollow?
A hollow cannot be measured with a tape round it, so it is measured across. Its girth is π × that diameter, and it is taken off by the same quarter-girth rule as the log: (π × diameter ÷ 4)² × length. Enter the hollow’s diameter and the calculator does this for you.
How is the CFT of sawn timber calculated?
Length in feet × width in inches × thickness in inches ÷ 144. A plank 12 ft long, 6 in wide and 2 in thick is exactly 1 CFT. In metric, length in metres × width in millimetres × thickness in millimetres ÷ 1,000,000 gives cubic metres.
How many CFT are in one CBM?
One cubic metre is 35.3147 cubic feet, so multiply CBM by 35.3147 to get CFT, or divide CFT by 35.3147 to get CBM.
Why does my supplier’s CBM not match my CFT?
Suppliers often state log volume on a diameter scale such as JAS, while the yard measures girth by the quarter-girth method. The two methods give different figures for the same log, and that difference — the variation — is worth tracking log by log.
Measuring every log by hand?
Timbba scans each log at the gate and the saw and works out its volume for you — purchase against mill, log by log, with the total for every lorry.