Pile Cap Calculator
Concrete, two-way bottom steel, formwork and blinding per cap.
With the default inputs: Cap length 2.4 · Cap width 2.4 · Cap height 1.2 etc.Total cap concrete 56.40 m³
Edit the inputs below to recalculate.Inputs
Result
| Concrete per cap | 6.912m³ |
| Total concrete with waste | 56.40m³ |
| Bottom bars (both ways) | 17 + 17bars |
| Bottom steel per cap | 193.0kg |
| Total bottom steel | 1544.0kg |
| Steel per m³ | 27.9kg/m³ |
| Formwork per cap | 11.52m² |
| Total formwork | 92.2m² |
| Total blinding | 5.41m³ |
Bar count = effective width ÷ spacing, rounded up, plus one: 2.4 m wide with 50 mm cover and 150 mm spacing gives 16 spaces and 17 bars. Rounding down would exceed the spacing. Bar length is cap size less two covers; hooks, pile-head anchorage and bends are not included — add them if needed. Only bottom steel is counted, so the steel rate here is lower than reality; pile caps typically run 60-110 kg/m³ overall. Caps need no soffit formwork since they sit on the blinding, so formwork is the four sides only.
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Formula
| Concrete per cap | V = length × width × height |
| Total concrete | V = V × count × (1 + waste) |
| Bars per direction | n = ⌈(side − 2 × cover) ÷ spacing⌉ + 1 |
| Steel weight | W = bars × length × dia² × 0.00617 |
| Formwork | S = 2 × (length + width) × height |
| Blinding | V = (length + 2 × projection) × (width + 2 × projection) × thickness |
How to work it out
- Single cap = length × width × depth; total = single × count × (1 + waste).
- Bottom bars n = ⌈(side − 2 × cover) ÷ spacing⌉ + 1 in each direction. Round up, because bars run to the edge.
- Bar length = side − 2 × cover + 2 × bend (typically a 10d upstand or none).
- Formwork = 2 × (length + width) × depth × count; all four faces are formed and the soffit is blinding, not formwork.
- Blinding = (length + 2 × projection) × (width + 2 × projection) × thickness × count.
Where it goes wrong
- Deriving bar count by dividing area by spacing — the correct count is ⌈clear span ÷ spacing⌉ + 1, one more at each edge. A 2.4 m cap gives 16 bars per direction, not 15, so two are lost per cap.
- Omitting top and side bars — caps on three or more piles normally have top reinforcement, and deep caps have side bars; measuring only the bottom can understate steel by 30-50%.
- Treating cap formwork like a pad footing — caps are buried with soil around them and often use side forms only, or brick earth forms, which are priced quite differently.
Material and cost
C30-C35 concrete runs 420-550 per m³, reinforcement 4,200-5,000 per tonne, brick earth forms 80-120 per m² (cheaper than timber and not struck). A 2.4×2.4×1.2 cap holds about 6.9 m³ of concrete and 0.6-1.0 t of steel.
On site
- Bottom bars must avoid pile heads, and pile starter bars are anchored into the cap (typically 35d-40d); that steel is routinely missed.
- Caps deeper than 1 m need mass-concrete temperature control and a single continuous pour.
- Set out pile cut-off levels consistently — 50 mm of error at the blinding leaves the cap short of its effective depth.
Basis
- GB 50007-2011 Code for design of building foundations, Section 8.5 (pile cap detailing)
- JGJ 94-2008 Technical code for building pile foundations, Section 4.2 (cap design and detailing)
- GB 50202-2018 Standard for acceptance of building foundation construction, Chapter 5
FAQ
Why is the steel rate so far below typical?
Why add one to the bar count?
Does a cap need soffit formwork?
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Pile Cap Calculator. 2026-10-25. https://jianzhujisuan.com/en/pile-cap