Enter slab width, cover, bar diameter, and count in seconds for instant. Get center spacing, clear gaps, checks, and printable summaries with downloads included.
The calculator distributes parallel bars across a member width using edge cover and optional tie diameter. The edge bar centerline offset is:
edge_offset = cover + tie_dia + bar_dia / 2
The effective centerline width available between edge bars is:
effective_width = member_width − 2 × edge_offset
If you enter a bar count (n), the center-to-center spacing is:
center_spacing = effective_width / (n − 1)
Clear spacing between adjacent bars is:
clear_spacing = center_spacing − bar_dia
A practical minimum clear gap target is checked using:
min_clear = max(user_min_clear, bar_dia, 25 mm, 1.33 × agg_size)
| Member width | Cover | Tie dia | Bar dia | Bars | Center spacing | Clear spacing |
|---|---|---|---|---|---|---|
| 1000 mm | 40 mm | 0 mm | 12 mm | 10 | ~ 102.2 mm | ~ 90.2 mm |
| 36 in | 1.5 in | 0.25 in | 0.5 in | 8 | ~ 4.29 in | ~ 3.79 in |
Rebar spacing controls crack width, load transfer, and durability. Bars placed too close restrict concrete flow and reduce consolidation, while bars placed too far apart may increase cracking and deflection. A spacing check is a quick way to improve constructability before drawings are issued.
Center-to-center spacing is the distance between bar centrelines and is convenient for layout. Clear spacing is the free gap between adjacent bars and is critical for concrete placement. This calculator reports both, helping you translate drawings into site-friendly dimensions.
Edge bars are not placed at the concrete face. Cover and tie diameter shift the first bar inward, reducing usable width. For example, a 40 mm cover and 12 mm bar reduces each edge by 40 + 0 + 6 = 46 mm, which lowers achievable spacing for a fixed bar count.
Common slab reinforcement layouts often fall between 100 and 200 mm center spacing, while larger members may use 150 to 300 mm depending on design and bar size. For shrinkage and temperature steel, tighter spacing with smaller bars is often preferred to spread cracking and ease placement around inserts. These are practical ranges only; final spacing must follow project drawings and governing standards.
Concrete must pass between bars without segregation. A practical target is to keep clear spacing at least the bar diameter, at least 25 mm, and roughly 1.33 times the nominal maximum aggregate size. This tool flags when your clear spacing drops below that target.
When you provide a desired spacing, the calculator selects a bar count that does not exceed your requested center spacing after accounting for cover and ties. This approach avoids over-crowding while keeping distribution uniform across the member width.
The optional estimate multiplies bar count by run length and applies a lap or waste allowance percentage. Unit weight is approximated using d²/162 (d in mm) to give kg/m. It is suitable for fast takeoffs, not a bar-bending schedule replacement.
Before fixing steel, confirm cover blocks, verify clear spacing at congested zones, and ensure tie diameter is reflected in edge offsets. If the minimum clear spacing check fails, adjust bar size, increase member width, or revise bar count to maintain workable gaps.
Member width, cover, tie diameter, and main bar diameter drive the effective width. Bar count or target spacing then determines the final layout. Enter accurate cover and tie values to avoid optimistic spacing results.
A FAIL means your clear spacing is below the practical minimum target based on bar size, aggregate size, and any user limit. Reduce the number of bars, use smaller bars, or increase the member width.
Use center spacing for layout and drawing coordination. Use clear spacing to judge concrete flow and congestion. If you only know one, this calculator converts to the other using the bar diameter.
Yes. Ties shift the first and last main bars inward because cover is measured to the outer steel. Including tie diameter reduces effective width, which reduces spacing for a fixed bar count across the member.
It is a fast approximation using d²/162 for unit weight and a simple lap allowance factor. It supports preliminary cost and procurement checks. For purchasing and fabrication, rely on a detailed bar schedule.
Yes, for any situation where parallel bars are distributed across a width. Use the appropriate member width and cover for the element. For multiple layers or bundled bars, evaluate each layer separately.
Enter your project limit in the user minimum clear spacing field. The calculator will use the maximum of that value and the other practical checks. Always confirm compliance with the governing code and drawings.
Build safer concrete with correct rebar spacing every time.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.