Concrete calculator
Preliminary slab rebar count, linear footage and bar-weight planning from spacing, cover and bar size.
By Feroz Sheikh · Formula CONC-REBAR-001 v1.0.0 · Tested formula
CONC-REBAR-001v1.0.0Enter your measurements. Switching units converts the same project, including coverage and unit rates. Package yields keep the unit printed beside each field.
Calculated result
Rebar to order
CONC-REBAR-001(floor(usable width ÷ long spacing) + 1) × usable length + (floor(usable length ÷ cross spacing) + 1) × usable width × (1 + waste)
Long bars
Cross bars
Net linear quantity
Planning estimate, not engineering advice. Confirm site measurements and product specifications. Calculation limits.
This calculator returns a preliminary slab rebar grid: bar count, linear feet and planning weight from spacing, cover and bar size. Formula CONC-REBAR-001 v1.0.0. Waste covers laps and cuts. Add the line to an estimate. It is not a placing drawing or a structural size.
Size chart
Planning grid only. Bar size and spacing come from the approved design.
| Slab | Primary | Check |
|---|---|---|
| 10 × 10 ft | 149 ft | 7 bars |
| 12 × 12 ft | 206 ft | 8 bars |
| 16 × 16 ft | 380 ft | 11 bars |
| 20 × 12 ft | 353 ft | 8 bars |
| 20 × 20 ft | 606 ft | 14 bars |
Metric example — 6 × 4 m grid. A 6 × 4 m slab at 18 in centres, #4 bar and 10% waste, returns 375 ft. Not a placing drawing.
Enter supplier prices and any labour, equipment or delivery costs. Pick a currency — badges, inputs, and totals follow.
Enter your supplier’s ready-mix concrete rate in the selected unit. Add delivery, pumping, short-load fees and placing labour as separate project costs. For GCC projects, select QAR, AED, SAR, KWD, OMR or BHD and enter local supplier rates.
How this calculator works
Feroz SheikhWritten by Feroz Sheikh · founder
This calculator lays a simple orthogonal rebar grid into a rectangular slab, using stated on-center spacing, edge cover and a published bar unit weight, then applies a visible lap-and-cut allowance.
This is a grid takeoff: spacing, cover, bar size and lap as visible inputs. It does not invent a structural schedule. The result is a planning cut list and weight, not a stamped drawing.
This separate example uses the calculator's starting values in imperial units. It stays unchanged when you edit the tool above. Example rates, yields and dimensions are assumptions, not recommendations for your project.
| Input | Example value |
|---|---|
| Slab length | 20 ft |
| Slab width | 12 ft |
| Long-bar spacing | 18 in |
| Cross-bar spacing | 18 in |
| Edge cover | 2 in |
| Bar size | #4 · 0.668 lb/ft |
| Lap and cut allowance | 10 % |
Example result: Rebar to order — 353 ft.
(floor(usable width ÷ long spacing) + 1) × usable length + (floor(usable length ÷ cross spacing) + 1) × usable width × (1 + waste)
Use the labelled units above when reproducing this example. To work in metric, switch the calculator to Metric; applicable measurements are converted, while product-specific units remain labelled.
Need the broader workflow? Read the concrete planning guide.
How-to: How to calculate a concrete slab · How to plan a slab rebar grid
Questions
No. Bar size, spacing, cover, laps and development length must come from the responsible design. This tool only estimates a rectangular grid quantity.
Rebar is often purchased by weight. Nominal unit weights follow published CRSI designations and remain visible so they can be replaced with mill data.
A 20 × 12 ft slab at 18 in each way, #4 bar and 10% lap waste, returns 353 ft. This is a planning grid, not a placing drawing.
No. Bar size is an input from the approved design. The calculator only counts and weighs the grid you describe.
This rebar calculator publishes formula CONC-REBAR-001, version 1.0.0. The ID stays on the result and on the estimate line.