Rebar Weight Calculator — kg/m, lb/ft & Bar Schedule

The weight of a reinforcing bar comes from one physical identity — the same W = ρ · A · L used for any steel member — but rebar has a convention that trips people up: the ribs do not count. Every standard (ABNT NBR 7480, ASTM A615, EN 10080, ISO 6935-2) defines the nominal mass of a deformed bar from the plain-round equivalent cross-section, i.e. from the nominal diameter d, ignoring the deformations that give the bar its grip:

kg/m = (π/4) · d² · ρ · 10⁻⁶ = 0.006165 · d² (d in mm, ρ = 7850 kg/m³)

So a 10 mm bar is 0.006165 × 10² = 0.617 kg/m, a 16 mm bar is 0.006165 × 16² = 1.578 kg/m, and a 25 mm bar is 3.853 kg/m — exactly the numbers printed in the NBR 7480 table. Multiply the unit mass by the bar length and the number of bars to get the order weight:

Total weight = (kg/m) × length (m) × number of bars

Two consequences worth remembering. First, because the ribs are excluded, a scale will read a real bar a percent or two heavier than the nominal — that difference is inside the rolling tolerance the mill is allowed. Second, the coefficient scales with the square of the diameter: doubling the bar size quadruples the weight per metre, which is why a handful of large bars can outweigh a forest of small ones. This calculator stores the published nominal mass of every size in all three standards, so you never approximate — you read the certified figure and it is multiplied out for you, live, with a dimensioned ribbed-bar sketch beside it.

This is the reference the other free calculators do not give you: the same bar in three coding systems, side by side, each with its own certified nominal mass. Brazilian CA-50 bars are named by their diameter in millimetres; US bars carry an eighth-inch bar number (#4 = 4/8″ = ½″); European bars use the metric diameter with a Ø prefix. The rows below are aligned by the closest diameter — note that they are close but rarely identical, which is exactly why a substitution needs the mass delta, not a guess.

*40 mm is a standard CA-50 diameter but is outside this tool's 5–32 mm picker; the value is listed for reference. The live Tri-norm equivalence card in the calculator does this automatically for whatever bar you pick — it names the nearest bar in the other two standards and prints the mass difference, so replacing a specified #5 with 16 mm CA-50 (+1.7% steel) or Ø16 (identical) is a decision, not a guess.

1. Pick the standard — Brazil CA-50 (ABNT NBR 7480), USA Grade 60 (ASTM A615/A615M) or Europe B500 (EN 10080). The bar-size grid updates to that system, each button showing the size and its unit mass in the active units.
2. Pick the bar size. The kg/m (or lb/ft) is the certified nominal value — the one your supplier invoices — not a re-derived approximation.
3. Enter the length per bar and the number of bars. The result updates instantly, no button: total weight in kg, tonnes and lb, plus the unit mass and the substituted formula with your own numbers.
4. Read the Tri-norm equivalence card to see the nearest bar in the other two standards and how much heavier or lighter it runs — the tool for converting a foreign spec or sourcing an import substitute.
5. Check the procurement panel — weight per bar, bars per tonne, metres per tonne, and how many stock lengths (12 m by default; set 20 ft / 40 ft for US practice) you must buy to cut your pieces.
6. Add a price per kg (optional) to turn tonnage into cost in your currency.
7. Switch to Bar schedule to build a full bill of bars — one row per bar mark, with mass and total length rolled up — and export it to CSV free, no watermark, ready for the estimate spreadsheet. The Add to bar schedule button on the Single-bar tab drops the current bar straight into the list.

The SI ⇄ imperial toggle converts every field — kg/m ↔ lb/ft, m ↔ ft, mm ↔ in — while the math always runs in SI internally, so the numbers round-trip exactly.

Brazil — CA-50 (ABNT NBR 7480). "CA-50" means concreto armado, characteristic yield 500 MPa. Bars are ribbed (high bond) and named by nominal diameter: 5.0, 6.3, 8.0, 10.0, 12.5, 16.0, 20.0, 25.0, 32.0 mm (40 mm also standardized). CA-60 (600 MPa) covers the thin welded-mesh wires. The nominal masses — 0.154 kg/m at 5 mm up to 6.313 kg/m at 32 mm — are the NBR 7480 Tabela 1 values, and the standard permits a mass tolerance of roughly ±6% on the thinnest bars tightening to ±4% for 10 mm and larger.

USA — Grade 60 (ASTM A615 / A615M). The imperial bar number is the diameter in eighths of an inch: #3 = 3/8″, #4 = 4/8″ = ½″, #8 = 8/8″ = 1″. So #3 through #11 step through 3/8″…1‑3/8″, then #14 (1¾″) and #18 (2¼″) for heavy columns. The nominal weight is defined directly by the standard in lb/ft — 0.376, 0.668, 1.043, 1.502, 2.044, 2.670, 3.400, 4.303, 5.313 for #3–#11 — and the "soft-metric" A615M designation restates each bar in millimetres (#4 → #13M, #5 → #16M, #8 → #25M).

Europe — B500 (EN 10080 / ISO 6935-2). "B500" is a bond-ductility class at 500 MPa (B500A, B500B, B500C differ in ductility). Preferred diameters are 6, 8, 10, 12, 14, 16, 20, 25, 28, 32, 40 mm, each with the same 0.006165·d² nominal mass — Ø12 is 0.888 kg/m, Ø16 is 1.578 kg/m, Ø25 is 3.853 kg/m. Note that Europe standardizes Ø12 and Ø14, which fall between the Brazilian 12.5 mm and the US #4/#5 — a reminder that the three systems interleave rather than align.

Across all three, the base metal is the same carbon steel at 7850 kg/m³; only the diameter ladder and the naming differ, which is precisely what the tri-norm table and the equivalence card reconcile for you.

The two questions people search most — "how much does #4 rebar weigh per foot" and "how much does 12 mm rebar weigh per metre" — are the unit mass itself. Here is the US ladder both ways, exact from ASTM A615:

And the metric ladder (CA-50 / EN, per metre): 8 mm — 0.395, 10 mm — 0.617, 12 mm — 0.888, 12.5 mm — 0.963, 16 mm — 1.578, 20 mm — 2.466, 25 mm — 3.853, 32 mm — 6.313 kg/m. To go from per-foot to per-metre multiply by 1.488 (1 lb/ft = 1.488 kg/m); to go the other way multiply kg/m by 0.672. A useful procurement check: a tonne of 10 mm bar in 12 m lengths is about 135 bars (1000 ÷ 0.617 ÷ 12), and a tonne holds 1,621 m of it regardless of cut length — both are printed live in the procurement panel.

Weight is arithmetic; whether the reinforcement is legal is design. This calculator crosses that line. Enter a rectangular section (width b, height h, effective depth d), the concrete strength fck and the steel grade fyk, and for the bar you picked it evaluates the two checks every detailer runs against the code that matches the bar system:

• Minimum and maximum steel area — is the provided Aₛ = n · Abar between Aₛ,min and Aₛ,max? The floor stops a brittle, under-reinforced section; the cap (typically 4 % of the gross concrete area, or the tension-controlled limit in ACI) keeps the section ductile and buildable. NBR 6118 uses the ρmin table (17.3) and 4 %·Ac; ACI 318-19 uses max(0.25√f′c/fy, 1.4/fy)·b·d for the minimum and the εt ≥ 0.005 tension-controlled ratio for the maximum; EN 1992-1-1 (EC2) uses max(0.26·fctm/fyk, 0.0013)·b·d and 4 %·Ac.
• Development length ℓb and lap length ℓs — how far the bar must be embedded to develop its yield force, and how long a splice must be. NBR and EC2 take the bond route ℓb = (φ/4)·(fyd/fbd) with fbd from the concrete tensile strength and a ribbed-bar bond factor; ACI uses its √f′c development equation. For φ16 at fck 25 all three land near 38–40 φ (~600–650 mm) — the sanity figure a rebar detailer carries in their head. Laps default to the common >50 %-lapped factor (Class B / α = 1.5).

These are the published code equations, with the modelling assumptions (ribbed high-bond bar, good bond position, straight anchorage, adequate cover and spacing) stated on the panel. Treat the output as a preliminary check to size and sanity-test the reinforcement — the governing project code and full detailing still rule. No free rebar-weight tool does this; it is what turns a catalog into a design aid.

Three more things a spreadsheet cannot do:

• Area-match substitution. You specified 5·Ø20 (Aₛ = 1571 mm²) but the yard only has Ø16. How many? The substitution engine resizes the whole group — n = ⌈Aₛ,source / Abar,target⌉ = 8·Ø16 (1608 mm², +2 %) — and prints the area actually delivered, the over-provision, the clear spacing in your section width, and the steel-mass and cost delta of the swap across your currency and supplier price. It works within a code or across all three systems, so a foreign Ø-spec becomes a local bar count, not a guess.
• Saved projects. A named bar schedule is stored in your browser and reopened later — and it round-trips through a portable JSON file, so the same schedule moves between machines, sessions and teammates. The Add to bar schedule button on the Single-bar tab feeds the same project. A schedule stops being a throwaway.
• Branded PDF bar-bending schedule. Beyond the free CSV, export a drawing-office PDF: a CalcSteel header, the dimensioned ribbed-bar sketch, the full schedule table with per-mark mass (and cost when priced), the roll-up totals, and — when you have run a section check — the As,min/As,max and ℓb/ℓs strip embedded on the page. Same technical-drawing export doctrine as the FEM tools, free and watermark-free here.