Rebar Calculator
Calculate linear feet and weight of rebar reinforcement for concrete slabs, walls, and foundations.
Formula & Explanation
Rebar reinforcement is laid in a grid pattern across concrete slabs and walls. The number of bars in each direction depends on the slab dimensions and bar spacing. Number of Bars Along Length = ceil(Width ÷ Spacing) + 1 Number of Bars Along Width = ceil(Length ÷ Spacing) + 1 Total Linear Feet: Linear Feet = (Bars Along Length × Length) + (Bars Along Width × Width) Rebar Weight: Weight = Linear Feet × Weight per Linear Foot for Bar Size Typical rebar weights (nominal): - #3 bar: 0.376 lb/ft - #4 bar: 0.668 lb/ft - #5 bar: 1.043 lb/ft - #6 bar: 1.502 lb/ft - #7 bar: 2.044 lb/ft - #8 bar: 2.67 lb/ft
Assumptions
- •Rebar is laid in a two-way grid pattern (bars run both directions)
- •Bars start 1 foot from edges (reflected in the +1 factor in bar count)
- •Bar spacing is uniform in both directions
- •Weights are nominal values for standard deformed rebar; actual weights vary slightly by mill
- •The calculator counts linear feet of each individual bar; total includes all bars in both directions
- •#4 and #5 bars are most common for residential concrete; #6-#8 for heavier structures
Example Calculation
A 20 ft × 15 ft slab with #4 rebar bars spaced 12 inches apart requires approximately 635 linear feet of rebar, weighing about 425 pounds.
Inputs
Results
Rebar Requirements for Common Slab Sizes (#4 bars, 12" spacing)
| slab_size | linear_feet | weight_lbs |
|---|---|---|
| 10 × 10 ft | 220 | 147 |
| 15 × 15 ft | 480 | 320 |
| 20 × 15 ft | 635 | 424 |
| 20 × 20 ft | 840 | 561 |
| 30 × 30 ft | 1860 | 1243 |
Frequently Asked Questions
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