Formwork Turnover Calculator
Initial formwork area and replacement allowance from total area and cycles.
Quick answer
With the default inputs: Total contact area 1000 m² · Planned cycles 6 cycles · Loss per cycle 5% etc.Initial formwork area 188.7 m²
Edit the inputs below to recalculate.Inputs
Result
Initial formwork area
188.7m²
| Total contact area | 1000.0m² |
| Cycles | 6cycles |
| Cumulative factor | 5.298 |
| Replacement over the run | 132.5m² |
| Total area purchased | 321.2m² |
| Sheets for first set | 64sheets |
| Sheets including replacements | 108sheets |
| Area per sheet | 2.977m² |
| Sheets per m² incl. replacement | 0.108sheets/m² |
Loss covers edge trimming and breakage only, not waste from poor setting out. Flipping plywood extends life by 2-3 cycles; levering forms off with a crowbar is the main cause of loss, and proper striking tools halve it.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
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.
How to work it out
- Establish the total contact area: measure the face in contact with concrete — beams take soffit plus two sides (not deducting slab thickness), slabs take soffit, columns four faces, walls two faces.
- Set the number of reuses. Plywood 6-8, bamboo ply 8-10, modular steel 50+, aluminium 200+. The figure depends on material, striking time and care.
- Area per set = total area ÷ reuses. That is what must be on site simultaneously — an investment figure, not a total.
- Allow replacements: every strike and re-erection damages edges, adds holes and distorts panels. Take 3-8% per cycle; cumulative replacement = set area × rate × cycles.
- Round the set area up to whole sheets (2440 × 1220 = 2.98 m²) and add 5% for irregular locations and patching.
Where it goes wrong
- Buying the whole area at once — 1000 m² bought outright against 6 reuses needs only about 170 m², tying up five times the capital plus storage and double handling.
- Assuming the theoretical maximum reuse — plywood rated at 10 cycles is typically scrapped at 5-6 on site after pry damage, rain swelling and unused holes, so 10 guarantees running short.
- Applying the loss rate once instead of per cycle — damage happens every cycle, so the calculation must compound rather than subtract once.
- Ignoring programme — where several work fronts run simultaneously, the set is sized by the number of fronts, not by the reuse count.
Material and cost
15 mm plywood 45-75 CNY per sheet (15-25 CNY/m²), bamboo ply 60-95, modular steel hire 0.8-1.5 CNY/m² per day, aluminium 1000-1500 CNY/m² to buy or 25-40 per m² per cycle to hire.
On site
- Strike on the strength of companion-cured cubes, not on days. Side forms come off when the arris will not spall; soffits need the specified percentage of design strength.
- Clean, oil and stack panels after every strike; well-kept boards give two or three extra cycles.
- Aluminium has a high entry cost but over 200 reuses; on a high-rise with 20 or more typical floors it beats plywood on overall cost.
Basis
- GB 50666-2011 Code for construction of concrete structures, Chapter 4 (formwork)
- JGJ 162-2008 Technical code for safety of building formwork
- GB 50204-2015 Code for acceptance of concrete structure construction, Chapter 4
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.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Formwork Turnover Calculator. 2026-10-25. https://jianzhujisuan.com/en/formwork-turnover
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.