Estimates a rebar grid laid across a rectangular slab, spaced evenly in both directions — the standard approach for slab reinforcement estimates.
How it works
The number of bars running in each direction is found by dividing each span by the bar spacing and adding one for the starting bar; the total pieces and total length are then summed.
What this does not include
This does not include structural engineering decisions like rebar grade, spacing requirements, or load calculations — actual spacing and grade depend on load requirements and local building code, which a structural engineer should specify.
How to use this calculator
- Enter the slab’s length, width, and desired bar spacing.
A worked example
A 10×10 ft slab with rebar on 12-inch spacing: 11 bars across the length, 11 bars across the width, 22 total pieces, 220 total feet of rebar.
What the variables mean
| Variable | Meaning |
|---|---|
| Length, width | Slab dimensions, in feet |
| Spacing | Distance between rebar centers, in inches |
Edge cases worth knowing
Bar count is one more than the number of spacing gaps, not equal to it. A 10-foot span at 12-inch spacing has 10 gaps but 11 bars, since a bar sits at both the start and end of the span, not just between the gaps.
A missing length makes the calculation impossible, so the calculator declines to show a result without it.
Frequently asked questions
Why does the bar count add one extra bar?
A grid needs a bar at both the starting edge and after every spacing interval — dividing the span by spacing gives the number of gaps, and adding one accounts for the starting bar.
Does this calculator determine what spacing I should use?
No — spacing is a structural engineering decision based on load requirements and local building code; this tool estimates material needed for a spacing you specify.
What’s a practical use for the total length figure?
Estimating how many standard-length rebar sticks to order, since rebar is typically sold in fixed lengths (like 20 feet) that need to be planned against the total length needed.
