Rebar Calculator
Slabs, footings, walls, columns, and beams. Bar schedule with linear metres, weight, and lap allowances per bar size.
Standard: 40x diameter (e.g. 10 mm bar = 400 mm lap). Structural: 50x.
Standard UK stock lengths: 6 m or 12 m. Used to calculate number of full bars to order.
Structural Elements
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Results
Total Linear Metres
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metres (inc. laps & waste)
Total Weight
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kg
Total Bars
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@ 12 m stock
Elements
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scheduled
Element Breakdown
| Element | Type | Description | LM (net) | LM (inc. laps+waste) | Weight (kg) |
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Bar Schedule - by Diameter
| Bar dia. | Weight/m | Net LM | With laps+waste | Weight (kg) | Stock bars (@ 12 m) |
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Frequently Asked Questions
How much rebar do I need for a concrete slab?
Divide slab length by bar spacing and add 1 to get bar count in one direction; multiply by slab width for linear metres. Repeat for the other direction and add the totals. For T12 at 200 mm centres, you need approximately 10 lm per m² of slab (5 lm each direction). Add 10% for laps and waste.
What diameter rebar should I use for a concrete slab?
T10 at 200 mm centres suits lightly loaded domestic floor slabs. T12 at 150-200 mm centres for more heavily loaded slabs or longer spans. Bar diameter and spacing must be confirmed by a structural engineer for any loadbearing application. BRC fabric mesh (A193 or A252) is a common alternative to individual bars.
What is the minimum concrete cover to rebar under UK Building Regulations?
Per Eurocode 2 (BS EN 1992-1-1): internal floor slabs (exposure XC1) minimum 25 mm cover. Foundations in contact with soil (exposure XC2) minimum 40 mm cover. Coastal/exposed environments require greater cover. Always add a 10 mm construction tolerance to the nominal cover specified.
What is the lap length for rebar?
Typically 40d to 50d (40-50 times the bar diameter). For T12: minimum lap 480-600 mm. For T10: minimum lap 400-500 mm. Values vary with concrete grade, bar position and exposure class - always refer to the structural design for project-specific lap lengths.
What is the difference between T bar (high yield) and R bar (mild steel) rebar?
T bars (deformed high yield, grade B500B) have a 500 MPa yield strength and a ribbed surface for better concrete bond - now the standard for UK structural concrete. R bars (mild steel, smooth, 250 MPa) are rarely specified for structural work but used for links in some applications. New structural designs should use T bar (B500B) unless otherwise specified.
What waste allowance should I use for rebar?
Add 10% waste for cutting, laps and on-site offcuts. Rebar is typically supplied in 6 m or 12 m lengths - calculate full lengths needed after applying waste. For complex shapes with many short bars, use 15%. Order a small surplus as cut-to-length steel can take time to re-order.