Rebar Calculator

How much rebar do I need?

ft
ft
in
in
Bar size
Stock length

Order this much #4 rebar

2020 ft bars

Grid both ways with 5% extra. Laps use a common 40 bar diameter rule. Plans and your engineer set bar size, spacing and splices.

#4 bar at 16 in on center, both ways10 × 16 bars
Bars along the length10
Bars across the width16
Total steel379 ft
Lap at splices20 in
Weight253 lb

Grid a slab both ways and see how many stock bars to buy, with laps and steel weight counted.

How it works

Bars each way come from slab size minus edge clearance ÷ spacing. Spliced runs add 40 bar diameters per lap, and 5% covers cuts.

Before you order

  • Keep steel up on chairs so it sits in the slab instead of on the base.
  • Hold bars about 3 inches off soil and off edges as a starting clearance, or as your plans state.
  • Stagger laps so splices do not stack in one line.

Common questions

How far apart should rebar be in a slab?

Residential slabs commonly use 12 to 18 inches, and your plans should set the actual number.

How long is a rebar lap?

A common rule is 40 bar diameters, or 20 inches for #4 bar. Structural drawings override rules of thumb.