# Rebar Spacing and Bar Count Calculator

Bars and actual spacing from run length and design spacing, with total weight.

- Page: https://jianzhujisuan.com/en/rebar-spacing
- Category: Rebar (https://jianzhujisuan.com/en/c/rebar)
- Chinese version: https://jianzhujisuan.com/zh/rebar-spacing.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Run length 6000 mm, Design spacing 200 mm, Bar diameter 12 mm, Cover each end 25 mm, Layers 1 levels): **Number of bars 30 bars**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Run length | number | 6000 | mm |  |
| Design spacing | number | 200 | mm |  |
| Bar diameter | number | 12 | mm |  |
| Cover each end | number | 25 | mm |  |
| Layers | number | 1 | levels |  |

## Formula

- **Net run**: L = run − 2 × cover
- **Bar count**: n = floor(L ÷ spacing) + 1
- **Actual spacing**: s = L ÷ (n − 1)
- **Total weight**: W = n × L × unit weight

## Worked example

A 6000 mm run with 25 mm cover at 200 mm spacing, 12 mm bars: 5950 mm net gives 30 bars at 205.2 mm actual spacing, 178.5 m total and 158.5 kg.

## Questions

### Why 30 bars and not 29?

Both ends carry a bar, so the count is always the number of spaces plus one. 5950 ÷ 200 = 29.75 gives 29 full spaces and therefore 30 bars. Forgetting the plus-one is the classic error, and across hundreds of beams it adds up to tonnes of steel.

### How far from the edge does slab reinforcement start?

Half a spacing, not one cover. At 200 mm spacing the first bar sits 100 mm from the beam or wall face. Support moments are high at the edge and bars set too far in leave an unreinforced strip, while half a spacing is also easier to work around. Rafts and wall boundary elements follow similar rules — read the drawing notes.

### Is slightly wider spacing acceptable?

Tolerances exist (typically ±10 mm and not more than 5% of design), but wider spacing means less steel per metre and lower capacity. If rounding pushes you past the tolerance, add a bar rather than spreading the spacing evenly.

## Related tools

- [Rebar Weight Calculator](https://jianzhujisuan.com/en/rebar-weight): Pick a bar diameter, enter length and quantity to get weight per metre, per bar and total tonnage.
- [Rebar Anchorage Length Calculator](https://jianzhujisuan.com/en/rebar-anchorage): Basic and seismic anchorage length from bar grade, diameter and concrete class.
- [Rebar Lap Length Calculator](https://jianzhujisuan.com/en/rebar-lap): Lap length ll / llE by splice percentage, plus the permitted number of splices.
- [Rebar Cut Length Calculator](https://jianzhujisuan.com/en/rebar-cut-length): Cut length and bar weight with standard hook allowances.
- [Stirrup Length and Count Calculator](https://jianzhujisuan.com/en/rebar-stirrup): Stirrup length, count and weight with the 11.9d seismic hook allowance.
- [Rebar Mesh Weight Calculator](https://jianzhujisuan.com/en/rebar-mesh): Weight per square metre and total mesh weight from dimensions and spacings.

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