How much concrete to order, not how much is drawn CONCRETE

Three things sit between the drawing and the delivery ticket

Every one of them has sent somebody back to the yard for another half metre, on a day when the gang is standing there and the first load is going off.

The volume itself. A slab is easy. A footing with a step in it, a pad with a haunch, a set of steps, a circular base: that is where people stop measuring and start estimating. Adding the shapes up one at a time is only arithmetic, and doing it on a page rather than on the back of the drawing means the working survives to be checked and argued with.

The overdig. A trench cut by machine is not the width on the drawing. A hundred millimetres either side of a six-hundred-wide footing is a third more concrete than the drawing says. This is the single most common reason a pour runs short, and it is entirely predictable: the bucket is the width the bucket is. Measure what was actually dug, not what was specified.

The waste allowance. Some stays in the barrow, some goes on the ground, some is left in the chute, the levels are never perfectly even and the last barrow is never quite enough. Five per cent is normal for a clean slab on level ground; ten is realistic for footings in a trench you are pumping into.

Order the right amount in the right direction

The asymmetry is what should drive the decision. Over-ordering costs the price of a part load and the trouble of getting rid of it. Under-ordering costs a cold joint in the middle of a pour, a second delivery charge, and an hour of the gang doing nothing, and on a structural element a cold joint may be a defect that has to be cut out.

So round up, and round up to whatever the supplier actually sells. Ready-mix comes in quarter or half metre steps depending on the plant; the honest figure to work from is what the ticket will say, not the number the arithmetic produced.

Tell the plant what it is for as well as how much. The mix, the slump and the aggregate size follow from whether it is a footing, a slab you will power float, or something being pumped forty metres, and a supplier given the job will get that right more reliably than one given only a number.

Keep the working

Print or save the breakdown and put it with the job file. Two reasons, both practical. When the pour runs over or under, the breakdown shows which figure was wrong (was the overdig underestimated, or did a shape get measured twice?), and that is how the next estimate gets better instead of being another guess with more confidence.

And when somebody asks why two and a half metres were ordered for a hole that looks like two, the answer is on one page with the overdig and the waste named, rather than being a matter of recollection. That conversation happens more often than the arithmetic does.

Nothing is uploaded. Nearby: CUT turns a cutting list into which bar each piece comes off, with the kerf counted; PALLET packs a load; FIGURES handles the rounding without quietly losing a tolerance; and COSTS turns the quantities into money.