Rebar Calculator
Count grid bars, total length and stock bars from a specified spacing.
Last reviewed September 19, 2026
Result
Buy 15 stock barsEstimate
No cutting allowance is added by default. Use Custom if your cutting plan needs one; lap and hook lengths must come from the reinforcement schedule.
- Bars running lengthwise, per layer
- 8
- Bars running widthwise, per layer
- 14
- Total rebar length
- 289 ft
- Length with cutting allowance
- 289 ftEstimate
https://calcgallery.com/concrete/rebar-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use it
- Enter the rectangular grid length and width from the reinforcement drawing.
- Enter the specified edge cover and bar spacing.
- Set the number of grid layers and the stock length sold locally.
- Read the bars in each direction, total length and estimated stock count.
How it is calculated
Cover is removed from both edges. The remaining distance is divided by the requested maximum spacing, rounded up, and one boundary bar is added:
Lengthwise bars = ceil(usable width ÷ spacing) + 1
Widthwise bars = ceil(usable length ÷ spacing) + 1Each direction is multiplied by its run length and by the number of layers. Stock quantity is total length divided by stock length, rounded up.
Safety and ordering
This calculator counts a reinforcement layout supplied by someone else. It does not design a slab, choose a bar diameter, decide spacing or certify compliance.
Make a cutting schedule. The headline stock count is the mathematical lower bound after the selected allowance. List each required piece against available stock before ordering.
Keep cover real. Chairs, spacers and tying hold the grid where the drawing expects it. Steel on the ground does not gain cover when concrete is poured over it.
Treat laps separately. A lapped grid is longer than its plan dimensions. Use the lap lengths specified for the job rather than a generic rule of thumb.
With your numbers
- 8 lengthwise and 14 widthwise bars per layer
- 1 layer = 289 ft total
- With 0% cutting allowance = 289 ft
- Rounded up to 15 stock bars
Quick reference
No cutting allowance is added by default. Use Custom if your cutting plan needs one; lap and hook lengths must come from the reinforcement schedule.
| Job | Stock bars to buy |
|---|---|
| 20 × 10 ft, 18 in spacing | 15 |
| 20 × 20 ft, 18 in spacing | 28 |
| 12 × 12 ft, 12 in spacing | 15 |
| 30 × 20 ft, 12 in spacing, two layers | 123 |
| 6 × 3 m, 450 mm spacing | 15 |
| 8 × 5 m, 300 mm spacing | 47 |
Common questions
- How much rebar is in a 20 ft by 10 ft grid at 18 in spacing?
- With 3 in edge cover, one layer has 8 bars running lengthwise and 14 running widthwise, totalling 289 ft before cutting allowance.
- Does this choose bar size or spacing?
- No. Enter those from the reinforcement drawing. Choosing reinforcement requires loads, concrete strength, support conditions and applicable code.
- Are lap splices included?
- No. Lap, hook, bend and development lengths depend on bar size and design requirements. Add them through a custom allowance only when you know the required lengths.
- Why is stock-bar quantity only an estimate?
- It divides total length by stock length as if every offcut can be reused. A real cutting schedule can require more bars, especially when full-length runs exceed one stock bar.