Edge clearance affects count
Rebar should not run directly to the form edge. Clearance and cover requirements reduce the usable grid dimension.
construction
Rebar Calculator
Estimate rebar sticks for a rectangular reinforcement grid.
20 ft rebar sticks120.00 square feet
- Waste / coverage
- 24 in grid spacing
- Area
- 120.00 ft²
Last reviewed: May 12, 2026 by the BuilderCalc editorial team.
SSR formula reference
Rebar Calculator formulas
These formulas are rendered in the server HTML so crawlers, LLMs, and users can read the method without running JavaScript. The interactive calculator can change the inputs, but the estimating math below is visible in the raw page source.
Volume (cubic feet) = Length x width x thickness (in inches / 12).
Volume (cubic yards) = Cubic feet / 27.
Bags (80-lb) = Cubic feet / 0.60, rounded up.
80-lb bag yields about 0.60 ft3, or 0.022 yd3.
| Result | Formula |
|---|---|
| Bars each direction | floor((slab dimension - 2 x edge clearance) / spacing) + 1 |
| Total bar length | sum of bars in both directions x bar run length |
| Stock sticks | ceil(total bar length / stock bar length) |
Standard PSI by application
| Application | Recommended PSI |
|---|---|
| Patio or walkway | 3,000 PSI |
| Garage floor, residential | 3,500 PSI |
| Driveway, cars | 3,500 to 4,000 PSI |
| Driveway, trucks or RVs | 4,000 to 4,500 PSI |
| Foundations and footings | 3,000 to 4,000 PSI, per plan and code |
Bag yield reference
| Bag size | Common yield |
|---|---|
| 80-lb bag | About 0.60 ft3, or 0.022 yd3 |
| 60-lb bag | About 0.45 ft3, or 0.017 yd3 |
| 50-lb bag | About 0.375 ft3, or 0.0138 yd3 |
| 40-lb bag | About 0.30 ft3, or 0.011 yd3 |
Reinforcement planning
Rebar Calculator planning notes
Rebar estimates depend on grid spacing, edge clearance, lap requirements, and stock length. Use the calculator as a planning count, then verify the final layout.
Lap and waste are separate
Long runs may need overlapping bars. Add lap length and cutting waste after the base grid count.
How to use it
Keep the estimate tied to field measurements
Set grid dimensions
Use the reinforced area after accounting for edge clearance and concrete cover.
Choose spacing
Enter spacing in each direction based on the project design, not only a generic rule of thumb.
Account for laps
Long runs may need overlapping bars and cutting waste after the base count is known.
Related calculators
FAQ
Concrete estimating questions
How do I estimate rebar for a slab?
Estimate bars in each direction based on slab dimensions, edge clearance, and spacing. Then account for stock length, laps, and waste.
What rebar spacing should I use?
Common slab grids may use 12, 16, or 18 inch spacing, but spacing depends on slab design, loads, and local requirements.
Does the calculator include lap splices?
Use the result as a planning count. Long runs may need lap length added based on bar size and project requirements.
Can wire mesh replace rebar?
Sometimes, but reinforcement choice depends on slab use, thickness, cracking control, loads, and local practice.