Takeoff and the waste factor

A calculator gives you an exact number. A jobsite never is. The gap between the two has a name — waste — and forgetting it is what sends you back to the supplier mid-pour.

Why the exact number is always short

Material gets lost on the way into the work: concrete left in the truck and the wheelbarrow, drywall offcuts around windows, tile that breaks, a board with a bad end. None of it ends up in the job, but all of it leaves your truck.

So every takeoff has two numbers: the net quantity the tool calculates, and the gross quantity you actually buy.

The waste factor

You add a percentage on top of net to cover the loss. Typical allowances:

• Concrete: 5–10%
• Drywall and lumber: 10–15%
• Tile, simple layout: 10% — diagonal or lots of cuts: 15–20%

A 33.3 ft³ slab at 10% waste: 33.3 × 1.10 = 36.6 ft³ to order.

Then round to what you can actually buy

You don't buy 36.6 cubic feet — you buy whole bags, whole yards, whole sheets. Always round up to the purchase unit:

• 36.6 ft³ ÷ 0.60 ft³ per bag = 61 bags → buy 61 (there's no 0.6 of a bag)
• 36.6 ÷ 27 = 1.36 yd³ of ready-mix → order 1.5 yd³ (most plants sell in quarter- or half-yard steps)

Order short and the whole crew waits while someone drives for one more bag. Build the waste in, round up, and the job keeps moving.