Timber in India is usually bought and sold by the cubic foot (CFT). A carpenter measures length in feet and the width and thickness of the section in inches, so the calculation mixes two units. Getting the conversion right is the difference between the right quantity and an expensive mistake.
The formula
Total CFT = CFT of one piece × number of pieces
Why 144? Width and thickness are in inches. To turn each into feet you divide by 12, and doing it twice means dividing by 12 × 12 = 144. The result is then in cubic feet.
Worked examples
EXAMPLE 1 · RAFTERS
Five pieces, each 8 ft long with a 4 × 2 inch section.8 × 4 × 2 ÷ 144 = 0.444 cft per piece
0.444 × 5 = 2.22 cft
EXAMPLE 2 · DOOR FRAME (CHAUKHAT)
A 7 × 3 ft door with a 4 × 2½ inch frame, three sides (no sill).Frame length = 7 + 7 + 3 = 17 ft
17 × 4 × 2.5 ÷ 144 = 1.18 cft, before any allowance for joints
EXAMPLE 3 · LENGTH IN INCHES
A 30-inch piece of 3 × 3 inch section: first convert length to feet, 30 ÷ 12 = 2.5 ft.2.5 × 3 × 3 ÷ 144 = 0.156 cft
Quick reference
Common sections, per running foot of length:
| Section (in) | CFT per running foot | CFT for 10 ft |
|---|---|---|
| 2 × 2 | 0.028 | 0.28 |
| 3 × 2 | 0.042 | 0.42 |
| 4 × 2 | 0.056 | 0.56 |
| 4 × 2½ | 0.069 | 0.69 |
| 5 × 2½ | 0.087 | 0.87 |
| 4 × 3 | 0.083 | 0.83 |
| 6 × 3 | 0.125 | 1.25 |
Each figure is simply width × thickness ÷ 144.
Converting to other units
- Cubic metres: CFT ÷ 35.315. So 10 cft = 0.283 m³.
- Metric sections: convert millimetres to inches first (÷ 25.4), or work fully in metres: length (m) × width (m) × thickness (m) = m³.
How much extra to buy
The formula gives the finished volume. Timber is lost to sawing, planing, end trimming, knots and splits, so buy more than you calculate. How much depends on the wood, how it is supplied (rough-sawn or planed) and the job. Discuss the allowance with your timber merchant; many carpenters add a margin for joints and wastage on every order.
Common mistakes
- Mixing units: entering length in inches but treating it as feet makes the answer 12 times too big.
- Nominal vs actual size: a "4 × 2" bought planed may measure less. Measure what you are actually buying.
- Forgetting the number of pieces: calculate one piece, then multiply.
Do it on your phone
The NANDIX wood CFT calculator handles several sizes at once, adds a rate per CFT for the cost, and lets you speak the measurements: "8 feet length, 4 inches width, 2 inches thickness, 5 pieces".
