Rebar Calculator
Estimate reinforcing-bar grid lines, total length, stock pieces, intersections, tie wire and material cost for a rectangular slab.
Default project preview
19 stock bars
Long-direction lines
9
Cross-direction lines
14
Grid intersections
126
Estimated bar weight
247.3 lb
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Slab length
Enter this project assumption in ft. The current imperial default is 20 ft.
Slab width
Enter this project assumption in ft. The current imperial default is 12 ft.
Bar spacing
Enter this project assumption in in. The current imperial default is 18 in.
Edge cover
Enter this project assumption in in. The current imperial default is 3 in. Minimum: 0.
Lap and cut allowance
Enter this project assumption in %. The current imperial default is 10 %. Minimum: 0. Maximum: 50.
Stock bar length
Enter this project assumption in ft. The current imperial default is 20 ft.
Bar weight
Enter this project assumption in lb/ft. The current imperial default is 0.668 lb/ft.
Price per stock bar
Enter this project assumption in a unitless value. The current imperial default is 12. Minimum: 0.
How to read the outputs
Long-direction lines
18 in spacing. Default preview: 9.
Cross-direction lines
perpendicular grid bars. Default preview: 14.
Grid intersections
potential tie points. Default preview: 126.
Estimated bar weight
entered bar weight. Default preview: 247.3 lb.
Tie wire guide
planning allowance. Default preview: 1.6 lb.
Material cost
full stock bars. Default preview: $228.00.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Grid lines = round up (clear dimension ÷ spacing) + 1. Total length = lines × perpendicular clear length, then lap and cut allowance is applied. Stock bars are rounded up.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 29, 2026
This calculator estimates reinforcing-bar runs, total length and purchasing quantity from slab or wall dimensions and entered spacing. It does not choose bar size, spacing, lap length, cover or reinforcement design.
Calculation steps
- 1Determine the clear reinforced dimensions after edge cover.
- 2Calculate bar-run count in each direction from the entered spacing.
- 3Multiply run count by each run length.
- 4Add lap and cutting allowance, then divide by stock-bar length and round up.
Worked numerical example
A 20 ft × 16 ft slab with bars at 12 in each way needs 17 runs in one direction and 21 in the other before edge-cover adjustment. The resulting cut lengths are then increased for laps and waste and rounded to full stock bars.
Purchasing and rounding
Rebar is purchased in fixed stock lengths or fabricated schedules. Offcuts are reusable only when their length, bend condition and project requirements allow it.
Interpret the result
A high stock-bar count can result from short stock lengths or conservative lap allowance rather than unusually dense reinforcement.
Page-specific assumptions
- Straight orthogonal bars.
- Uniform spacing.
- Laps are represented by the entered allowance.
- Chairs, ties and bent bars are estimated separately.
Common mistakes
- Treating spacing as a structural recommendation.
- Counting spaces instead of bars.
- Ignoring concrete cover.
- Assuming every offcut can be reused.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Rebar Calculator questions
Does every rebar intersection need a tie?+
Tie requirements depend on the reinforcement plan and placement method. The intersection count is a planning reference.
What edge cover should be used?+
Required concrete cover depends on exposure, placement against soil, member type and code.
Does this calculate rebar design?+
No. Bar size and spacing must come from an approved structural design.