Concrete Wall Calculator — Volume, Formwork & Rebar
Pour volume, formwork area, form ties, release agent and reinforcement for a cast-in-place wall. Order ready-mix by volume or count bags, and spread the formwork over the number of pours the panels will serve.
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How the concrete wall calculator works
- 1Net area = length × height, less openings; volume = net area × thickness, plus waste
- 2Ready-mix is ordered by volume, rounded to how the plant sells it; bags instead = volume ÷ the yield printed on the bag
- 3Formwork = gross area × 2, because a wall is formed on both faces. Openings are not deducted: a panel runs past a box-out rather than stopping at it
- 4Divide that area by the number of pours the panels will serve to get what you actually buy
- 5Ties on a grid: area ÷ (horizontal spacing × vertical spacing)
- 6Rebar: a bar at each spacing in both directions, times the layers, plus laps. Weight = π/4 × diameter² × 7,850 kg/m³ — 490 lb/cu ft, the density of steel and the one fixed constant in the whole calculation
- 7Release agent = formwork area ÷ the coverage stated on the tin
Worked example
18 m × 2.4 m wall, 200 mm thick (59 × 8 ft, 8 in), one layer of 12 mm bar at 200 mm both ways — a #4 at 8 in — with 5% waste.
8.64 m³ in place and 9.1 m³ ordered (11.9 cu yd). 86.4 m² of formwork — 930 sq ft — 155 ties, and 478 m of bar weighing 424 kg: 1,568 ft and 935 lb. That works out at 49 kg per m³ of wall, the middle of the band real walls sit in.
Frequently asked questions
Why is the formwork area twice the wall, with openings left in?
Formwork is contact area, and a wall is formed on both faces. Openings stay in because a panel runs past a window box-out rather than being cut around it — deducting them would under-order the one material you cannot be short of on pour day.
Bags or ready-mix?
Bags are realistic up to roughly a cubic metre, about 1.3 cu yd — and that is already some 100 bags of 20 kg (44 lb). Above it ready-mix is cheaper, stronger and far faster, and a wall wants pouring in one go. Both are priced here, so the crossover is visible rather than assumed.
Does it take US bar sizes?
Enter the diameter and the weight follows from it: a #4 bar is 12.7 mm, a #5 is 15.9 mm. Spacing, thickness and wall size all read in feet and inches with the EU/US toggle, and prices in your own currency.
Plan the whole job
One calculation is one line of a job. With the floor planner you draw the room once and every calculator on the site fills itself from those measurements, with the openings taken off. The project manager then holds every room and trade against one budget, and tracks what things actually cost as the invoices arrive.