Slab Rebar Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
100% FreeRuns in your browserIntermediate
Enter Values
Enter your values and press Calculate to see results.
How to use this calculator
- Enter the slab length and width (m) and the bar spacing (mm).
- Read the bars each way and total length.
How it works
Bars each way = slab dimension ÷ spacing + 1; total length sums both directions of a single mat.
Worked example
5 × 4 m slab at 200 mm. 21 + 26 bars, ~209 m total.
Common mistakes
- Forgetting laps, trim/edge bars and chairs.
- Using this for structural design — bar size and spacing must come from an engineer.
Frequently asked questions
Does this size the bars?
No — it counts a mat at your chosen spacing. Bar diameter and spacing should be specified by a structural engineer.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.