Rebar Calculator
Lay out an orthogonal reinforcement grid for quantity planning. Enter slab dimensions, spacing, edge cover, layers, stock length, and allowance.
What does the rebar calculator calculate?
For each grid direction, divide the usable perpendicular dimension by spacing, round down, and add one bar. Multiply the bar count by its run length, repeat for each layer, and add laps and waste. Final spacing, size, cover, development, and support require approved structural details.
Orthogonal rebar grid quantity
Bar count in one direction is controlled by the perpendicular clear dimension. The calculator totals both directions, applies the number of layers, then adds allowance before converting linear feet into stock lengths.
How to measure for an accurate estimate
- Use grid dimensions, spacing, cover, and layers directly from approved reinforcement drawings.
- Measure clear run length inside the specified concrete edge cover.
- Treat beams, thickened edges, dowels, vertical bars, and separate mats independently.
- Prepare a bar schedule when stock lengths are shorter than runs or bends and hooks are required.
Single slab grid
A 20 ft by 12 ft grid has 18-inch spacing, 3-inch edge cover, one layer, 20-ft stock, and 10% extra.
The grid uses 317 linear ft before extra and 348.7 ft after extra, or 18 stock bars.Before you purchase material
- Order the specified bar grade, size, coating, and certification rather than substituting by diameter.
- Use an approved lap and development schedule; the percentage field is only a purchasing allowance.
- Include chairs, bolsters, tie wire, caps, couplers, and fabrication separately.
- Store reinforcement off the ground and arrange inspection before concrete placement.
Common questions
How do I count rebar in each direction?
Use the clear dimension perpendicular to the bars, divide by the specified spacing, round down, and add one. Then verify the final edge spacing and cover against the plan; layout adjustments may change the calculated count.
Does this rebar calculator include lap splices?
It includes only a user-selected percentage allowance for laps and cuts. It does not determine required lap length or splice location. Those depend on bar size, grade, concrete strength, coating, confinement, code, and structural details.
What rebar size and spacing should I use?
A quantity calculator cannot design reinforcement. Bar size and spacing depend on loads, slab geometry, concrete properties, soil support, crack-control needs, exposure, and code. Use stamped plans or obtain direction from a qualified structural professional.
Should rebar be placed directly on the ground?
No. Reinforcement must be held at its specified position and concrete cover during placement. Use approved chairs, bolsters, or supports suitable for the base and load; lifting a loose grid during the pour is unreliable.
Sources and reference standards
- Concrete Reinforcing Steel InstituteIndustry source explaining reinforced-concrete materials and placement fundamentals.
- International Code Council — 2024 International Residential CodePrimary model-code source for residential foundations, reinforcement, masonry, and stair safety requirements.