Rebar Calculator
Calculate rebar for strip foundation and monolithic slab: length and weight by diameter 8/10/12/14/16 mm.
Total length of all sides of the strip in meters
How many rebar lines run along the strip (top and bottom layers combined)
Higher loads need a larger diameter
Calculation formula
L = perimeter × rows × 2 (strip); L = 2 × (length × n_transverse + width × n_longitudinal) (slab); weight = L × ρ(d)
For strips, count longitudinal rebar in both top and bottom layers. For slabs, two grids (bottom and top) with the chosen spacing in both directions. Linear weight: 8 mm — 0.395 kg/m, 10 — 0.617, 12 — 0.888, 14 — 1.21, 16 — 1.58 kg/m.
About the rebar calculator
The rebar calculator computes total length and weight of steel bars for a strip foundation or a monolithic slab. For strip footings it accounts for longitudinal bars in both the top and bottom layers along the full perimeter. For slabs it estimates two reinforcing grids with the chosen spacing in both directions.
Enter the perimeter or slab dimensions, pick a diameter from the standard range 8, 10, 12, 14, 16 mm, and get the result in linear meters and kilograms. Weight is taken from the standard linear-mass table: 12 mm — 0.888 kg/m, 14 mm — 1.21 kg/m, 16 mm — 1.58 kg/m.
The result is a base estimate. Add 5–10% for lap splices at joints and another margin for cutting waste. For corners and L-junctions plan separate bent bars cut from the same rebar.
Why use this calculator
Two modes in one
Strip and slab modes use different formulas — switch instantly without reloading the page
Real linear-mass table
Weight is computed from the standard table for A500C-grade rebar from 8 to 16 mm
Browser-only math
All calculations run locally — your numbers never leave your device
Frequently asked questions
What rebar diameter do I need for a private house?
For a single-story house or bathhouse 12 mm longitudinal bars are typical, for two stories or a heavy roof 14 mm is preferred. Stirrups and slab grids are usually made of 8–10 mm bars.
Do I need tying wire or can I weld the cage?
Standard cages are tied with 1.2 mm annealed wire — this preserves bar strength and lets the cage flex. Welding is allowed only for weldable grades (A500C) and only spot-weld, otherwise the metal is overheated.
What grid spacing should I use in a slab foundation?
For a private house use 20 cm spacing in both directions; for heavy loads 15 cm. Going below 10 cm gives no benefit, and above 25 cm weakens the slab.
How do I lap-splice rebar correctly?
Splice bars with an overlap of 40–50 diameters: for 12 mm rebar that means 50–60 cm. Stagger the splices in a checkerboard pattern and keep them out of high-stress zones.