For a rough slab formwork estimate: plywood sheets = slab area ÷ 2.98 m² (one 1220 × 2440 mm sheet) plus 5–10% waste; secondary H20 beam running metres = (slab length ÷ beam spacing + 1) × slab width; primary beams the same way at their wider spacing. A 12 × 10 m slab needs about 43 sheets, 250 m of secondary beams and 72 m of primary beams. This is for pricing only, not design.
Step 1: plywood sheets
One 1220 × 2440 mm sheet covers 2.98 m². Divide the slab area by 2.98 and add 5–10% for cuts and damage.
Step 2: secondary beams
Rows of secondary beams = slab length ÷ spacing + 1. Running metres = rows × slab width. Spacing is often around 0.5 m; use your formwork design.
Step 3: primary beams
Primary beams run the other way at a wider spacing set by the design (often 1.5–2.5 m). Running metres = (slab width ÷ spacing + 1) × slab length.
Worked example: 12 m × 10 m slab
| Item | Calculation | Result |
|---|---|---|
| Area | 12 × 10 | 120 m² |
| Plywood sheets | 120 ÷ 2.98 = 40.3, plus 5% | about 43 sheets |
| Secondary beams (0.5 m) | (12 ÷ 0.5 + 1) × 10 | 250 running metres |
| Primary beams (2.0 m) | (10 ÷ 2 + 1) × 12 | 72 running metres |
Estimate for quotation purposes only. Beam spacing, prop layout and plywood thickness must come from a qualified formwork or temporary works design.
Turn it into an order
Send us the running metres and bay sizes. We split them into standard H20 lengths and quote beams, plywood and white wood together.