Rebar Spacing Count
Calculator
Results
- Bars across the width
- 21
- Bars along the length
- 31
- Total number of bars
- 52
- Total rebar length (m)
- 250
Construction results
| Bars across the width | 21 |
| Bars along the length | 31 |
| Total number of bars | 52 |
| Total rebar length (m) | 250 |
formula-map diagram
- Bars across the width
- 21
- Bars along the length
- 31
- Total number of bars
- 52
- Total rebar length (m)
- 250
Formula breakdown
Formula
n = floor(span ÷ spacing) + 1, both directions= 21
Note
Simplified model: results are quantity estimates only. They ignore openings, overlaps, cuts, site conditions and local building codes. Structural figures are not a substitute for a design by a qualified engineer.
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See all →Frequently asked questions
How does the calculator determine how many rebar pieces I need?+
It divides the span (length or width of the area to be reinforced) by your chosen spacing interval, then adds one to account for the bar at the starting edge — for example, a 10 ft span at 12 in (1 ft) spacing needs 11 bars, not 10.
Why does spacing matter so much for a slab's strength?+
Rebar spacing determines how effectively tensile loads are distributed across the concrete, since concrete is strong in compression but weak in tension. Wider spacing than specified reduces reinforcement in the gaps and can lead to cracking under load; tighter spacing than needed wastes material and adds cost.
Do I need rebar running in both directions?+
For most slabs, yes — a grid pattern with bars running both lengthwise and widthwise resists cracking and load in both directions, so the calculator typically needs to be run twice: once for each direction, using that direction's span and spacing.
Why is the +1 in the bar-count formula easy to overlook?+
Dividing span by spacing tells you how many gaps fit, not how many bars — since a bar sits at both the start and end of each gap, the total bar count is always one more than the number of gaps. Skipping this adds up to a meaningful shortfall on longer runs.
Does standard rebar come in a fixed length, and how does that affect ordering?+
Rebar commonly comes in 20 ft or 6 m stock lengths, so for spans longer than that you'll need to splice bars with an overlap (commonly 12-24 times the bar diameter), which increases the total linear footage needed beyond the simple span calculation.