Concrete planning · Updated November 3, 2026
Concrete slab rebar grid estimator
Count bars and estimate linear footage for a simple rectangular two-direction slab grid using your project dimensions, spacing and edge inset.
Count a simple rectangular two-direction bar grid from the dimensions and layout values on your project plan. Enter the spacing and edge inset specified for your project; this tool does not select them.
Enter values and calculate.
This is a geometric quantity estimate for a single rectangular mat. It does not determine bar size, strength, structural adequacy, lap lengths, hooks, chairs, support, placement or code compliance. Confirm the reinforcement plan with the project designer and local requirements.
Sources and method
- Concrete Reinforcing Steel Institute: Placing Bars (reviewed November 3, 2026): discusses bar spacing and concrete cover. Use the project documents to supply both layout inputs; this tool does not prescribe them.
- American Concrete Institute: Importance of Concrete Cover (reviewed November 3, 2026): explains that cover protects reinforcing steel from harmful influences. The required cover depends on project conditions and is not calculated here.
For bars running along the length, count = ceiling((slab width × 12 − 2 × edge inset) ÷ entered spacing across width) + 1. Their estimated cut length is slab length × 12 − 2 × edge inset. Repeat in the other direction. Total linear footage is the sum of both bar groups; the optional allowance applies to footage only. This does not assign stock bars or optimize cuts, laps or offcut reuse.
How it works
Enter the rectangular slab dimensions, the project-specified bar spacing across each dimension and the distance from each edge to the bar center. The calculator counts each bar direction from those inputs and totals linear footage. An optional allowance applies to footage only. It does not select reinforcement or check structural design.
Good to know
Quick answer: how do I estimate rebar for a rectangular slab?
For a simple two-direction grid, count each direction from the clear span, entered spacing and edge inset, then multiply the bar count by its estimated length. This estimator shows those steps and totals the linear footage from your inputs. It does not determine the reinforcement plan. Reviewed November 3, 2026.
What spacing and edge inset should I use?
Use the spacing and edge location specified by the project designer or plans. CRSI discusses bar spacing and concrete cover; required details depend on the project. This calculator does not recommend them.
Does this determine bar size or structural adequacy?
No. Bar size, grade, spacing, cover, reinforcement placement and structural adequacy must come from project documents and the qualified design professional. This tool only counts a geometric grid from values you enter.
Does the linear footage equal the number of stock bars to buy?
No. The total does not account for stock lengths, laps, hooks, bends, cut sequencing or reusable offcuts. Make a separate takeoff from the project details before ordering.
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