# Blinding and Cushion Calculator

Plan size, concrete volume and side formwork for blinding.

- Page: https://jianzhujisuan.com/en/cushion-layer
- Category: Concrete (https://jianzhujisuan.com/en/c/concrete)
- Chinese version: https://jianzhujisuan.com/zh/cushion-layer.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Footing base length 20 m, Footing base width 10 m, Projection per side 0.1 m, Blinding thickness 0.1 m, Number of pads 1 pcs, Formwork method Earth mould (no formwork), Concrete waste 2%): **Total blinding concrete 21.02 m³**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Footing base length | number | 20 | m |  |
| Footing base width | number | 10 | m |  |
| Projection per side | number | 0.1 | m | Usually 100 mm, 150-200 in poor ground |
| Blinding thickness | number | 0.1 | m | 100 mm typical, 150 on soft ground or large footings |
| Number of pads | number | 1 | pcs |  |
| Formwork method | select | Earth mould (no formwork) | — |  |
| Concrete waste | number | 2 | % |  |

## Formula

- **Blinding length**: L = footing + 2 × projection
- **Blinding width**: B = footing + 2 × projection
- **Volume per pad**: V = L × B × thickness
- **Total concrete**: V = V × count × (1 + waste)
- **Perimeter**: P = 2 × (L + B)
- **Side formwork**: S = P × thickness × count

## Worked example

A 20 by 10 m footing with 100 mm projection and 100 mm blinding, one pad, earth mould: blinding plan 20.20 by 10.20 m, 206.04 m², 20.60 m³ net, 21.02 m³ with waste, and 6.08 m² of formwork if shuttered on all sides.

## Questions

### Why project the blinding 100 mm?

Two reasons. Cover: bottom bars need concrete around them and room to tie, so the wider blinding keeps the mesh off the soil and makes fixing practical. Formwork: the footing shutters stand on the blinding and need space outside for braces and tie bolts, which 100 mm provides. In poor ground or with groundwater, use 150-200 mm so sloughing cannot eat into the blinding.

### Should blinding formwork be priced at all?

It depends on the method, not on a rule. Bills of quantities allow blinding formwork as a provisional item, but if the blinding is cast directly on the trimmed excavation (earth mould) there was no formwork, so claiming it is over-measurement that audit will cut. Judge from ground conditions and excavation: firm ground that trims cleanly suits an earth mould; fill, sand, or a base above existing level needs shuttering. Price it as none, state the method in the construction plan, and claim by variation if formwork was actually erected.

### How thick and how strong?

Normally 100 mm of C15 plain concrete. Thicken it to 150 mm for large footings with high soil reaction, or on soft and muddy ground — where it also needs a φ6 at 200 mm mesh and stops being plain concrete. With groundwater the blinding doubles as a waterproofing substrate, so it must be flat and thick enough to survive site traffic. Never go below C15; weaker blinding crumbles underfoot.

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- [Concrete Pour Sequencing Calculator](https://jianzhujisuan.com/en/concrete-pour-plan): Divide a slab into strips and get the volume, truck count and duration for each pour.
- [Concrete Strength Converter](https://jianzhujisuan.com/en/concrete-strength-convert): Convert between grade, MPa, psi and kgf/cm², with cube-to-cylinder correction.

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