Layout model and usable dimensions
This rebar calculator estimates an orthogonal grid in a rectangular slab after subtracting concrete cover at both ends. It rounds the number of spaces up so the actual grid spacing does not exceed the spacing entered. Bars longer than available stock are split into segments with an entered lap allowance. The purchase result assumes each grid line is cut independently, so it is a conservative takeoff rather than an optimized cutting schedule. Bar size, cover, lap and spacing must be supplied by the project designer.
Fit, direction and offcut constraints
- Hooks, bends, chairs, dowels and extra reinforcement around openings are excluded.
- The line count limits maximum spacing; actual evenly distributed spacing can be slightly smaller.
- Lap requirements vary with bar, concrete, location and design conditions.
Layout arithmetic and example
A worked example
For a 20 × 12 ft slab with 3 in cover and 18 in spacing, the grid has 9 lengthwise and 14 crosswise lines: 23 lines and 336.5 ft of bar before laps.
Total bar length is not a fabrication schedule
A 20-foot stock bar cannot provide an uninterrupted 22-foot line. The line needs a specified splice arrangement or a suitable longer stock length. Dividing the combined length of every grid line by stock length hides this constraint. The tool counts stock per line and includes the entered lap; sharing compatible remnants may reduce purchases, but requires a separate cutting plan.
Take lap, cover and spacing from the project design. Use the output to check quantities rather than select reinforcement.
Measure and compare a layout
- Enter slab dimensions and specified cover.
- Use the grid spacing and lap from the reinforcement schedule.
- Check cut lengths and stock counts with your supplier.
Frequently asked questions
Does it choose rebar spacing?
No. It estimates a grid using spacing and cover that you provide.
Why is stock count higher than total length divided by stock length?
The conservative count allows each line to use its own stock pieces. A cutting optimization may reuse offcuts.
Are overlapping bars included?
The specified lap is added for every splice needed when a grid line exceeds stock length.
Calculation method: JICWH methodology. Examples are planning assumptions, not product recommendations.