Stock bars to buy
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Concrete reinforcement material estimator
Rebar Calculator
Estimate rebar for slabs, pads, and simple footing runs. Enter slab size, spacing each way, stock bar length, lap/waste allowance, bar weight, and price to get bars each way, total length, sticks, weight, and cost.
Units
Bars each way
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Total length
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Steel weight / cost
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Rebar quantity is not structural design
Use the engineered drawings, local code, slab thickness, cover, chair height, dowels, hooks, corners, and inspection requirements for real reinforcement design. This calculator is only a material takeoff helper.
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Rebar calculator formula
Lengthwise bar count = floor(slab width ft ÷ (spacing in ÷ 12)) + 1
Cross bar count = floor(slab length ft ÷ (spacing in ÷ 12)) + 1
Base length = lengthwise bars × slab length + cross bars × slab width
Total length = base length × (1 + lap/waste %)
Stock bars = ceil(total length ÷ stock bar length)
Steel weight = total length × bar weight per length
Example
A 30 ft × 20 ft slab at 18 in spacing uses 14 bars running the 30 ft direction and 21 bars running the 20 ft direction. Base length is 840 ft. With 10% lap/waste, buy 47 twenty-foot sticks.
Rebar calculator FAQ
How do you calculate rebar for a slab?+
Count the bars running each direction from the slab size and spacing, multiply each count by the opposite slab dimension, add lap/waste allowance, then divide by the stock bar length. Round up because rebar is bought in full sticks.
What spacing should I use for slab rebar?+
Common field estimates use 12 inch, 16 inch, 18 inch, or 24 inch spacing, but the correct spacing and bar size must come from the engineer, plan, local code, soil, load, and slab thickness.
Does this include lap splices?+
Use the lap/waste allowance for overlaps, hooks, cutoffs, bends, and layout losses. This calculator estimates order quantity and weight; it does not design reinforcement.
Can I use this for footings?+
Yes for quick linear rebar takeoffs: enter footing run as length, footing width as the width field, and set spacing/count assumptions to match the plan. Use engineered details for exact bar layers, corners, dowels, and stirrups.