Construction

Rebar Calculator

Work out the bars and total rebar length for a slab grid.

Slab length

Slab width

Bar spacing

Edge clearance

Price per foot ($)

Calculated Output

Total bars (bars) 30

Total rebar length 400

Total cost ($) 0

Formula: bars per direction = floor((span − 2×edge)/spacing) + 1

Step-by-Step Breakdown

1. Values used:

2. Slab length = 20

3. Slab width = 10

4. Bar spacing = 12

5. Edge clearance = 3

6. Price per foot = 0 $

8. Total bars = Slab length + Slab width = 20 + 10 = 30bars

9. Total rebar length = 400

10. Total cost = 0$

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The math behind it

In each direction: bars = floor((span − 2×edge clearance) ÷ spacing) + 1.

Bars running the length span the width, and vice-versa. Total length = bars × the span they run.

20×10 ft slab, 12 in spacing, 3 in edge → ~11 + 21 bars, ~430 ft of rebar.

What rebar spacing for a slab?

Residential slabs commonly use #3–#4 bar at 12–18 in on center.