Rebar Spacing & Quantity Calculator
Linear feet of rebar needed for a slab grid, given dimensions and on-center spacing.
Result
How to use this calculator
- Enter slab length and width.
- Set the on-center spacing (typically 12-18 in).
- Adjust overlap if your slab spans more than one rebar length (rebar comes in 20-ft sticks typically).
About this calculator
A rebar grid for a slab needs one bar at each spacing interval in both directions, plus one at the edges. The overlap accounts for splice length where two pieces meet (typically 40 × bar diameter, or 1-2 ft for #4/#5 bar). Add waste yourself when you order — 5-10% covers cut-offs.
Frequently asked
What is "on-center" spacing?+
How thick of a rebar do I need?+
Should I tie or weld the bars?+
How much overlap is required at splices?+
Do I need rebar for a 4-inch patio?+
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