CFT Calculator: How to Calculate Cubic Feet for Timber, Sand & Stone

If you have ever bought wood, sand, marble or granite in India, you have almost certainly seen the bill priced in CFT rather than kilograms or square feet. CFT is the standard unit for measuring bulk material by volume, and getting it wrong, even by a small margin, can mean paying for material you never received or arguing with a supplier over a number neither of you can verify on the spot. This guide walks through exactly how CFT is calculated for different materials, with the formulas and examples you need to check any bill yourself.

What is CFT?

CFT stands for Cubic Feet, a unit of volume. One CFT is the volume of a cube measuring exactly 1 foot on each side, 1 ft x 1 ft x 1 ft. It is the default unit for pricing timber, firewood, sand, stone slabs, marble, granite and other bulk construction materials across most of India, largely because it maps neatly onto the imperial measurements still used on site: feet and inches for lengths, and a simple multiplication for volume.

The basic CFT formula

For any rectangular block, plank, slab or sawn piece of timber, the formula is straightforward:

The only rule that trips people up: every dimension must be in feet before you multiply. If a measurement is in inches, divide it by 12 first. Mixing units, say multiplying feet by inches directly, is the single most common source of wrong CFT figures.

Calculating CFT for round logs (girth method)

Sawn planks have flat, measurable faces, but a felled tree trunk does not. For round logs, timber traders use the girth method, where girth is the distance around the log's circumference, because it is far easier to wrap a tape around a log on site than to estimate its diameter accurately.

This formula essentially treats the log as if it were a square post inscribed within the circular cross-section, which is why the girth is divided by 4 rather than by π. It is a deliberately conservative estimate that has been standard practice in the timber trade for generations.

CFT for sand, aggregate and loose material

For loose material like sand or aggregate delivered by truck, CFT is usually calculated from the dimensions of the container or truck bed it fills, or measured against a standard reference: a truck body of known length, width and height is used to back-calculate the volume of material it can carry. Since loose material settles and compacts differently depending on moisture and grain size, CFT here is an approximation rather than an exact figure, which is why serious buyers cross-check delivered quantity against the agreed truck capacity rather than trusting a verbal estimate.

CFT for stone slabs, marble and granite

Stone slabs are usually priced by CFT as well, using the same rectangular formula, but the height (thickness) is where disputes usually happen since slabs are rarely perfectly uniform. Suppliers typically measure thickness at multiple points and average them, or round up slightly, which is worth checking before agreeing to a rate.

How CFT pricing varies by material

Two timber pieces with the exact same CFT figure can still sell at very different prices, because CFT only measures volume, not quality. When you get a quote per CFT, the rate itself is set by several factors layered on top of the raw volume calculation:

• Wood species: hardwoods like Teak and Sal command a higher rate per CFT than softer, faster-growing species like Mango or Rubber wood, because of density, durability and how long the tree takes to mature
• Grade and defects: knots, cracks, warping or insect damage lower the effective rate even though the CFT volume stays the same
• Moisture content: freshly cut, unseasoned wood is heavier and can shrink as it dries, so seasoned timber is usually priced differently from green wood of the same CFT
• Regional supply: the same species can price differently between states depending on transport distance from the source forest or plantation and local demand
• Sawing waste: a log's CFT and the CFT of the planks eventually sawn from it are not identical, since sawing always loses some volume as sawdust and offcuts

Because of this, always treat the CFT figure as the starting point of a negotiation, the volume both sides agree on, rather than the final price itself. The rate per CFT is a separate conversation that depends on the specifics above.

Quick reference: CFT formulas cheat sheet

Converting CFT to other units

Common mistakes that lead to wrong CFT figures

• Mixing feet and inches without converting, which is the most frequent error in manual calculations
• Using the rectangular formula on round logs instead of the girth method, which overstates the volume
• Rounding intermediate steps too early, which compounds small errors across a large order
• Not accounting for irregular thickness in stone or marble slabs
• Confusing CFT with cubic meters when comparing quotes from different suppliers

Why use an online CFT calculator instead of manual math

Manual CFT calculation is not complicated, but it is easy to make a small unit-conversion slip under pressure, standing in a timber yard with a supplier waiting for an answer. An online calculator removes that risk: enter the dimensions once, pick the right method for the material, and get an instant, repeatable result you can screenshot and keep as a record of the deal.

Key takeaways

CFT is simple in principle, a straight volume calculation, but the details that trip people up are almost always the same: forgetting to convert inches to feet, using the wrong formula for round logs versus sawn planks, and treating the CFT figure as a final price rather than the starting point for a rate negotiation that also depends on species, grade and moisture content. Whether you are buying a single plank or a full truckload of sand, re-measuring at least one dimension yourself and running the numbers independently takes a minute and can save a meaningful amount on a large order.

Frequently asked questions