Rebar Chair / Bar Support Calculator

Work out how many bar chairs you need to support a top mat. Enter the slab size and the chair grid spacing, and get the total number of chairs and the chairs-per-m² density.

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How to use: Rebar Chair / Bar Support Calculator

Enter slab length and width.
Set the chair grid spacing.
Read the total chairs required.

Formula

Chairs = (floor(L ÷ spacing) + 1) × (floor(W ÷ spacing) + 1).

See the full rebar weight chart (kg/m & lb/ft) →

Rebar Chair / Bar Support Calculator — FAQ

How many rebar chairs do I need?

Roughly one per square metre at 1 m spacing — the tool gives the exact grid count.

What spacing for bar chairs?

Commonly 1.0–1.2 m each way for slab top mats.