Formwork area
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m²
Free tool
Formwork Calculator — plywood sheets, area & lumber
Estimate the formwork contact area, number of plywood sheets, and linear metres of timber for a slab, strip, column, or pile-and-beam foundation. Switch between metric and imperial, add a waste margin for offcuts, and get an order-ready material list in seconds.
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Plywood sheets
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sheets
Lumber length
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m
How to use the formwork calculator
- Step 1
Pick your foundation type
Choose slab, strip, column, or pile + beam — each type has a different formwork geometry and the inputs update to match.
- Step 2
Enter the dimensions
Add length, width, thickness or height, and the number of elements, in metric or imperial units.
- Step 3
Choose your sheet size and spacing
Pick a standard plywood sheet size and the typical joist or stud spacing for your site.
- Step 4
Read the results
Get formwork contact area, number of plywood sheets, linear metres of timber, and an optional wood volume and cost estimate — all with your waste margin applied.
How the calculation works
The calculator first computes the concrete-to-formwork contact area from your foundation geometry. For a slab on ground this is just the edge perimeter (the bottom sits on the ground); for a strip foundation it is both the inner and outer vertical faces; for columns it is all four sides; for pile + beam it is the beam sides.
The contact area is then divided by the area of one plywood sheet to get the base sheet count. A waste margin (10–15% is typical for offcuts and irregular shapes) is applied on top. Lumber is estimated as the formwork area divided by your chosen joist spacing, giving the total linear metres of secondary beams or studs.
1220 × 2440 mm — Standard sheet
The most common plywood sheet size worldwide, giving 2.98 m² (32 ft²) per sheet. Other sizes like 1500 × 3000 mm are also available.
10–15% — Typical waste margin
Plywood offcuts, cuts around openings, and damaged sheets mean you rarely use every square centimetre. A 10–15% buffer keeps you from running short mid-pour.
Standard plywood sheet sizes
| Sheet size (mm) | Sheet size (ft) | Area (m²) | Area (ft²) |
|---|---|---|---|
| 1220 × 2440 | 4′ × 8′ | 2.98 | 32 |
| 1500 × 3000 | 5′ × 10′ | 4.50 | 50 |
| 1220 × 1220 | 4′ × 4′ | 1.49 | 16 |
1220 × 2440 mm (4′ × 8′) is the most common size and the default in this calculator. Always confirm availability with your local supplier.
Worked example: formwork for a 6 × 4 × 0.3 m slab (edges only)
A slab 6 m × 4 m × 0.3 m on ground needs edge formwork only: 2 × (6 + 4) × 0.3 = 6 m² of contact area. With 1220 × 2440 mm sheets (2.98 m² each) you need 6 / 2.98 ≈ 2.0 → 2 sheets base. Add 10% waste: order 3 sheets. For lumber at 0.5 m joist spacing: 6 / 0.5 = 12 linear metres of timber.
Foundation types & their formwork
Slab (monolithic)
Formwork area = perimeter edges only (2 × (L + W) × thickness). For a slab on ground, the bottom sits directly on the subgrade — no bottom formwork needed. This keeps the sheet count low compared to suspended slabs.
Strip
Formwork area = 2 × perimeter × height (both inner and outer faces). Uses far fewer sheets than a slab for the same footprint because only the wall faces are formed, not the trench bottom.
Column (isolated/pad)
Formwork area = 2 × (width + length) × height per column, multiplied by the number of columns. Four vertical faces per pad — small area per unit but adds up with many columns.
Pile + beam
Formwork area = 2 × beam perimeter × beam height for the sides of the ground beam. Piles are typically bored or driven and do not require traditional formwork — only the connecting beam is formed.
Frequently asked questions
How many plywood sheets do I need for formwork?
Divide the total contact area by the area of one sheet (2.98 m² for 1220 × 2440 mm) and add 10–15% for offcuts. For a 6 m × 4 m slab edge formwork (6 m²), that is 6 / 2.98 ≈ 2 → 2 base sheets, plus waste → 3 sheets to order.
What size plywood is used for formwork?
The most common size worldwide is 1220 × 2440 mm (4′ × 8′), giving 2.98 m² per sheet. Other standard sizes include 1500 × 3000 mm (5′ × 10′) and 1220 × 1220 mm (4′ × 4′). Use 18–21 mm thick plywood for most foundation formwork.
How much waste should I allow for plywood?
10–15% is typical for formwork plywood. Offcuts from corners, irregular shapes, cut edges, and occasional damaged sheets all contribute. This calculator lets you set your own waste margin.
How do I calculate the formwork area for a strip foundation?
Multiply the foundation perimeter by the height, then double it (for both inner and outer faces). For a strip 8 m × 6 m outer, 0.4 m thick, 0.8 m high: perimeter = 2 × 8 + 2 × (6 − 0.8) = 26.4 m, then area = 2 × 26.4 × 0.8 = 42.2 m².
Does this calculator work in imperial units?
Yes. Toggle to imperial to enter dimensions in feet and get formwork area in square feet, sheet counts for 4′ × 8′ sheets, and lumber length in feet. All formulas stay the same.
What's not included in this calculator?
This calculator estimates contact area, plywood sheets, and lumber length. It does not estimate props, shores, form ties, or clamps — those depend heavily on concrete pour height, pour rate, and site-specific engineering decisions that vary too much for a general-purpose online tool.
From the formwork → PinMy
Calculating the formwork is step one. On site, the questions pile up: was the formwork set square, did the ties hold during the pour, where is that cold joint? With PinMy you pin a photo, a voice note or a video on the exact spot of your plan, photo, or 3D model — so the record of every pour lives in one place.
Related
This calculator gives estimates for planning and ordering. Formwork design must be checked by a qualified engineer for your specific pour height, concrete pressure, and site conditions.