Formwork Area Calculator

In short Formwork is measured in AREA while concrete is measured in VOLUME, and the two do not scale together — which is the whole reason a formwork take-off is worth doing separately. A 6 by 4 metre slab 150 mm thick has 24 m² of soffit plus 3 m² around its four edges, so 27 m² of shuttering against 3.6 m³ of concrete: 7.5 square metres of form for every cubic metre poured. Halve the slab thickness and you halve the concrete while the soffit stays exactly the same size, so that ratio climbs to 14.2. Thin elements cost far more per cubic metre than their concrete suggests, and on a small job the formwork is usually the bigger line. The geometry differs by element and this page handles four. A slab is its soffit plus the perimeter times the thickness. A beam is two sides plus a soffit — the top is open. A column is all four faces. A wall is both faces, and the thickness only enters the volume. FACES THAT TOUCH NOTHING ARE NOT SHUTTERED, and neither are faces cast against ground or against an earlier pour, so they are not counted. Sheets are whole things. 27 m² plus a 10% cutting allowance is 29.7 m², and at 2.98 m² for a 2.44 by 1.22 metre sheet that is 9.98 sheets — so ten. The waste allowance covers cutting rather than breakage, and an awkward plan shape wants more of it than a rectangle does. The economics live in the reuses. Plywood is not consumed by one pour: spread ten sheets over five uses and the cost per pour is a fifth of the purchase price, which is why hiring panels only competes with buying ply on short jobs. AND THE LIMIT MATTERS MORE HERE THAN ON MOST PAGES. This is a take-off of contact area and sheet count. It says nothing about props, bearers, ties, or whether any of it will carry wet concrete. Falsework that fails is one of the more serious things that can go wrong on a site, and its design is not a question this page touches.