About this tool Calculate reinforcement quantities for concrete elements. Enter the bar size, spacing (or number of bars), element dimensions, and cover — the tool gives you the number of bars, cut length, total length and weight, lap count and lap length, and the area of steel provided.
Four element types are supported: slabs/rafts, walls/retaining walls (both using spacing-based layouts), and beams/columns (using a specified number of bars). The full BS 4449 bar size range is included from T8 to T40.
Lap lengths are calculated at 50 diameters — a conservative simplified tension lap that is safe for C30/37 and above per Eurocode 2 cl. 8.7. For lower concrete grades or specific bond conditions, always check the project structural drawings. The tool automatically determines how many laps are needed based on your selected stock bar length (6m or 12m).
How to use this tool 1. Select the element type — slab, wall, beam, or column. Slabs and walls use bar spacing; beams and columns use a bar count.
2. Choose the bar size — from T8 to T40. The dropdown shows diameter and weight per metre for each size.
3. Enter dimensions and cover — span/height, width (for slabs/walls), and concrete cover. The cut length is calculated by deducting cover from both ends.
4. Select stock bar length — 6m or 12m. If the cut length exceeds stock length, laps are automatically calculated.
5. Review the results — total weight (with and without laps) is the key figure for ordering reinforcement.
Technical information Bar sizes: BS 4449:2005+A3:2016 — T8, T10, T12, T16, T20, T25, T32, T40. Weight per metre calculated from nominal diameter using steel density of 7,850 kg/m³.
Lap length: 50 × bar diameter (simplified conservative tension lap per EC2 cl. 8.7.3, safe for concrete grade C30/37 and above with good bond conditions). EC2 actual lap lengths vary from 36ø to 71ø+ depending on concrete grade, bond conditions, bar position, percentage lapped, and confinement. Always refer to the project structural drawings for specified lap lengths.
Area provided (mm²/m) = bar area × 1000 / spacing
Limitations This is a quantity take-off tool, not a structural design tool. It calculates how much reinforcement you need for a given specification — it does not determine what bar size or spacing is required for a given load.
Cut lengths are simplified — cover is deducted from both ends but no bend allowance is included. For bars with hooks, bends, or cranks, add the appropriate allowance per your bar bending schedule.
The 50-diameter lap length is a simplified conservative value, safe for C30/37 concrete and above with good bond conditions. For lower concrete grades (e.g. C25/30), EC2 requires longer laps — up to 71ø in some cases. For concrete grades C50/60 and above, shorter laps may be permissible. Always refer to the project structural drawings for specified lap lengths.
Revision history 28 April 2026: Initial release
Disclaimer This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.
Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.
All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.
By using this tool, you accept full responsibility for how you interpret and apply the information provided.
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