Rebar Calculator
Calculate the total linear footage and exact piece counts of steel rebar needed to reinforce a concrete slab.
Slab Specifications
Reinforcement Results
Rebar Calculation Formula
Rows in one direction = Slab dimension Spacing (in feet)
Total linear ft = (Rows Length) + (Rows in perpendicular Width)
For estimation purposes only. Verify structural calculations with a licensed engineer.
Rebar Reference Guide
Concrete has high compressive strength but low tensile strength. Steel rebar provides the internal skeleton that prevents slabs from pulling apart. Use the table below to choose the right rebar size for your project.
| Rebar Size | Diameter | Common Use |
|---|---|---|
| #3 rebar | 3/8 inch | Light slabs, sidewalks |
| #4 rebar | 1/2 inch | Standard residential slabs |
| #5 rebar | 5/8 inch | Driveways, heavy slabs |
| #6 rebar | 3/4 inch | Structural foundations |
Standard Spacing Recommendations
- 4-inch slab (light duty): #3 rebar at 18-inch spacing
- 4-inch slab (driveway): #4 rebar at 12-inch spacing
- 6-inch slab (heavy): #4 or #5 rebar at 12-inch spacing
Remember that rebar must maintain at least a 3-inch "edge clearance" from the dirt or wooden forms to prevent the steel from rusting. Our calculator automatically subtracts this edge clearance when designing your grid. Also, when calculating manually, always factor in a 10% waste margin to account for lap splices (where two pieces of rebar overlap and tie together).