Formwork Turnover Calculator
Initial formwork area and replacement allowance from total area and cycles.
Inputs
Result
Formula
| Cumulative factor | S = Σ(1 − r)^(k−1) for k = 1…cycles |
| Initial area | A = total ÷ S |
| Replacement | A = initial × (cycles − S) |
| Sheets | N = ceil(initial ÷ sheet area) |
1000 m² of contact area over 6 cycles at 5% loss: cumulative factor 5.298, initial area 188.7 m², replacement 132.4 m² — 321.1 m² in total, or 64 sheets at 2440 × 1220.
FAQ
Why not just divide area by cycles?
Because forms are lost each cycle, so usable area decays rather than stepping down evenly. Plain division underestimates the initial purchase: at 1000 ÷ 6 = 167 m², only 129 m² survives to cycle six, forcing a mid-run purchase that costs more.
Plywood or steel forms?
Plywood is cheap, easy to work and suits irregular shapes, but only lasts 5-8 cycles so its amortised cost can exceed steel; steel lasts 30+ cycles and gives a better finish, but needs a big upfront spend, lifting gear and costly adaptation. Residential standard floors favour aluminium or steel, basements and irregular work favour plywood.
What loss rate is typical?
3-5% on well-run sites, 5-8% generally, and over 10% with poor control or many irregular shapes. Striking method dominates: levering, careless stacking and weather exposure all shorten life sharply. Raising and covering the stack and applying release agent can cut loss by 2-3 points for very little cost.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.