Rebar Calculator for Strip Foundations
Work out how much rebar a strip footing needs: longitudinal bars with an allowance for laps and corners, closed stirrups with hooks, stock bars to buy, and total weight in kg. You set the reinforcement layout; this tool lays it out over the footing length. It does not design the reinforcement.
Footing section
Reinforcement layout
Before you order
- This calculator lays out the reinforcement you've chosen. It does NOT check whether that layout is strong enough. Bar count, diameter and grade depend on soil, building loads and local codes, and need a structural engineer.
- Lap splices, corner L-bars and offcuts are covered by one percentage allowance (10% by default, as in builders' merchants' worked examples). If your drawings specify lap lengths — a design-code lap is often 40–80 bar diameters — or many corners and T-junctions, raise the allowance.
- Rebar is sold by weight, and real bars may differ from the nominal kg/m by a few percent (the standard allows about ±4–8%). Expect the metres you get per tonne to differ slightly from this estimate.
- Stirrup cut length includes a hook allowance of 24 bar diameters (IS 2502 shortcut). Bending shops may use a slightly different convention, so check against their cutting list.
How this is calculated
Longitudinal steel is the number of bars in the section times the total strip length (outer perimeter plus interior walls), plus a percentage allowance for lap splices, corner bars and offcuts. Each stirrup is a closed rectangle following the section minus the concrete cover on every side, plus 24 bar diameters for its two hooks; the number of stirrups is the strip length divided by the spacing, rounded up. Lengths are turned into weight with the nominal mass per metre for each bar diameter. That figure is the same for the Russian GOST 34028-2016 table and European B500 bars (steel density 7850 kg/m³). The stock-bar count is total metres divided by bar length, rounded up, with no cutting optimisation.
Common questions
Why doesn't it tell me which bar diameter to use?
Choosing bar size and count is structural design: it depends on soil bearing, wall loads and the local code, and getting it wrong is a real safety issue. Rule-of-thumb tables online disagree with each other. This tool deliberately only counts the material for a layout you (or your engineer) have already chosen.
Why are laps a percentage instead of being counted joint by joint?
Because an exact lap length is a design-code calculation (it depends on concrete class, steel grade and how many bars are spliced in one place), and builders' guides disagree on it — 30, 40 or more bar diameters. Worked examples from rebar suppliers instead add 5–10% for laps and offcuts, so the calculator does the same and lets you change the percentage.
Can I use this for US #4 or #5 bars?
Not directly. The bar list here is metric (10–25 mm longitudinal, 6–12 mm stirrups), as used in Europe, the UK, Russia and most of the world. US # sizes have different diameters and weights per foot (ASTM A615) and aren't included.
Part of Home Improvement Calculators