Rebar Calculator
Total rebar weight and stock-bar count from bar size, piece count, length, and a waste allowance.
Content updated September 14, 2026
Weight uses the fixed ASTM A615 nominal value for the selected bar size, which does not change with steel grade. Bar size, spacing, and layout are structural decisions — verify against approved plans and local code with a qualified professional.
Calculate total rebar weight from a standard US bar size (#3 through #18), the number of pieces you need, and the length per piece, then see how many full stock-length bars to buy after a waste and lap-splice allowance.
Weight comes from a fixed lookup table by bar size — not a geometric formula — which is what makes this calculation distinct from every volume or area estimate elsewhere on this site.
The Rebar formula
Total length = pieces × length per piece · order length = total length × (1 + waste% ÷ 100) · weight = order length × weight per foot (from bar size) · stock bars = ceiling(order length ÷ stock length)Length per piece is converted to feet before multiplying · weight per foot is a fixed ASTM A615 nominal value looked up by bar size, not calculated from a formula.
Worked example
20 pieces of #4 bar (0.668 lb/ft) at 10 ft each with a 5% waste allowance gives a total length of 200 ft, an order length of 210 ft, and a total weight of 140.28 lb (63.63 kg). At a 20 ft stock length that is 10.5 bars, rounding up to 11.
Assumptions, rounding, and limitations
Assumptions
- Weight per foot is the fixed ASTM A615 nominal value for the selected bar size and does not vary with steel grade.
- All pieces entered are the same bar size and length; different sizes or lengths must be calculated separately and added together.
- The waste and lap-splice allowance is applied as a flat percentage of total length.
Rounding: Length and weight math retain floating-point precision. Displayed figures show up to three decimal places; the stock-bar count always rounds the exact quotient upward to a whole bar.
Limitations
- Does not determine bar size, spacing, or layout — those are structural and local-code decisions.
- Mill-run weight can vary from the nominal value by up to about 6% under standard tolerance; use nominal values for takeoff and let your supplier reconcile tolerance at delivery.
- Does not model bends, hooks, or stirrup shapes, which use additional length beyond a straight cut.
Sources
- Bridge Construction Records & Procedures Manual, BCM 52-1 Attachment 3 — Reinforcing Steel Bar Chart — California Department of Transportation (Caltrans)
Weight is fixed by bar size, not calculated from a formula
ASTM A615, the US standard for deformed steel reinforcing bars, assigns each bar size a fixed nominal weight per foot that does not change with steel grade (40, 60, 75, 80, or 100) — only with the bar's nominal diameter. This calculator multiplies that fixed per-foot weight by your total ordered length.
Total length is pieces multiplied by length per piece, plus your entered waste and lap-splice allowance — the extra length needed for cutting waste and the overlap where two bars are spliced together.
From total length to bars to buy
Rebar is sold in stock lengths, commonly 20 ft or 60 ft depending on supplier and size, so the calculator also divides your order length by a stock length you enter and rounds up to the number of full bars you would actually need to buy or cut from.
Frequently asked questions
▶How much does rebar weigh per foot?
It depends on the bar size: for example a #3 bar is 0.376 lb/ft, a #4 bar is 0.668 lb/ft, and a #8 bar is 2.670 lb/ft, per the ASTM A615 standard. Weight does not change with steel grade.
▶How do I calculate total rebar weight?
Multiply the number of pieces by the length per piece to get total length, add your waste and lap-splice allowance, then multiply by the fixed weight-per-foot for your bar size.
▶What length does rebar come in?
Commonly 20 ft or 60 ft stock lengths, though this varies by supplier and bar size — confirm with your own supplier and enter that figure so the bar count is accurate.
▶Does bar size number mean anything specific?
Yes — for US bars, the size number is the nominal diameter in eighths of an inch, so a #4 bar is 4/8 = 0.500 inches in diameter.
▶Does this tell me what bar size or spacing I need?
No. Bar size, spacing, and layout are structural decisions that depend on the design load and local code — this calculator only totals weight and bar count for a size and quantity you already know.
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Open calculator →Disclaimer: Rebar Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.