Steel Weight Calculator
Calculate the total weight of steel reinforcement bars (rebar) given their diameter, length, and quantity. Standard quantity-take-off tool for reinforced concrete, using the well-known d²/162 formula derived from steel's density.
Last updated: May 2026
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About this calculator
The weight per metre of round steel bar is W/L = π · d² / 4 · ρ × 10⁻⁶, where d is bar diameter in mm and ρ is steel density ≈ 7,850 kg/m³. Substituting: W/L ≈ 0.00617 · d² kg/m. The often-quoted shortcut formula W/L = d²/162 comes from rearranging: 1/0.00617 ≈ 162. So a 12 mm bar weighs 144/162 ≈ 0.889 kg/m; a 20 mm bar weighs 400/162 ≈ 2.469 kg/m; a 25 mm bar weighs 625/162 ≈ 3.858 kg/m. The calculator extends this to a quantity of bars: W = (d² / 162) × L × N, where N is the number of bars of the same diameter and length. Result is total weight in kg. Variables: d = diameter in mm (standard rebar sizes: 6, 8, 10, 12, 16, 20, 25, 32, 40 mm in metric; #3 to #11 plus #14, #18 in US Imperial); L = length in metres; N = number of bars. Edge cases: the formula assumes plain or deformed round bar of standard structural steel (density 7,850 kg/m³); galvanised, stainless, or fibre-reinforced polymer (FRP) rebar have different densities. For epoxy-coated rebar the coating adds <1% to weight — negligible. The d² scaling means larger bars are dramatically heavier per metre: a 32 mm bar weighs 6.3× more per metre than a 12 mm bar. For a complete project takeoff, sum across all bar sizes, lengths, and quantities. Standard suppliers usually round up to the nearest tonne for shipping; round delivery quantities up to allow for cutting waste (typically 3–5%).
How to use
Example 1 — Slab reinforcement quantity. A floor slab uses 12 mm bars, each 6 m long, 80 bars total. W = (12² / 162) × 6 × 80 = 144/162 × 6 × 80 = 0.889 × 6 × 80 ≈ 426.7 kg. ✓ Round up to 430 kg for ordering; at typical $1,200/tonne rebar pricing, that's $516 in material plus delivery and bending fees. Example 2 — Column reinforcement. A column needs 6 main bars of 25 mm diameter, each 4 m long. W = (25² / 162) × 4 × 6 = 625/162 × 4 × 6 = 3.858 × 4 × 6 ≈ 92.6 kg. ✓ Add the column ties (10 mm bars, perimeter ~1.6 m, every 200 mm c/c over 4 m height = 20 ties): tie length per tie = 1.6 m, total = 20 × 1.6 = 32 m of 10 mm bar. W_ties = (100/162) × 32 × 1 ≈ 19.8 kg. Total column reinforcement ≈ 92.6 + 19.8 ≈ 112.4 kg per column.
Frequently asked questions
Why does the formula use d²/162 instead of d² × constant?
The d²/162 form is a shortcut derived from the underlying geometry and steel density. The cross-sectional area of a round bar is π·(d/2)² = π·d²/4 mm². Multiplying by 1 m length gives volume in mm²·m, then by steel density 7,850 kg/m³ and the appropriate unit conversion yields mass per metre ≈ 6.165 × 10⁻³ · d² kg/m for d in mm. Rearranged: d²/162 (where 1/0.006165 ≈ 162.2 ≈ 162). The 162 number is universally used in reinforced-concrete tables across British, European, and Indian practice. The formula slightly underestimates for deformed (ribbed) bars at the ribs (which add a small amount of mass) but the contribution is typically <2% and ignored in standard takeoffs.
What are standard rebar sizes and their unit weights?
Metric (European/British) sizes and their kg/m: 6 mm (0.222), 8 mm (0.395), 10 mm (0.617), 12 mm (0.888), 16 mm (1.580), 20 mm (2.470), 25 mm (3.858), 32 mm (6.321), 40 mm (9.875). US Imperial sizes use # designations: #3 (9.5 mm, 0.560 kg/m), #4 (12.7 mm, 0.994), #5 (15.9 mm, 1.552), #6 (19.1 mm, 2.235), #8 (25.4 mm, 3.973). The d²/162 formula handles any diameter you plug in. For non-circular sections (square or hexagonal bars, used in pre-stressing strands), area-based formulas apply instead. Standard structural rebar grades are B500B (Eurocode, 500 MPa yield) and Grade 60 (US, 60 ksi = 414 MPa yield); higher grades like B500C, Grade 80, Grade 100 exist for special applications.
How much waste should I add to a rebar quantity estimate?
Standard practice is 3–5% waste for cutting losses, lap splices (longitudinal bars in continuous elements need overlap zones, typically 40 bar diameters), and standard bending allowances. For complex shapes (heavily reinforced beam-column joints, post-tensioned anchorages, curved structures) waste can reach 10%. For long, continuous bars without splices, waste can be as low as 2%. The supplier's pricing usually assumes 5% waste built-in, so the d²/162-based calculation should be ordered at the nominal quantity for most jobs. For projects with significant cut-and-bend work done by the supplier (offsite fabrication), the supplier handles waste internally; for projects where bars are delivered straight and cut/bent on site, add the 5% waste yourself. Always specify in the order whether you want stock-length straight bars or shop-fabricated cut-and-bent bars, as the latter cost 20–40% more but eliminate site labour.
What are the most common mistakes engineers make with rebar weight calculations?
The first is unit confusion: entering diameter in cm or m instead of mm gives results that are orders of magnitude wrong. The second is forgetting lap splices — long continuous bars often need overlap zones that add 5–10% to the total bar length, depending on the bar size and concrete grade. The third is using net bar length (between supports) instead of including the bent/hooked ends; standard rebar drawings specify bar shape, and the total bar length includes all bends and end hooks. The fourth is forgetting transverse reinforcement (stirrups, ties, links) which can account for 30–50% of total rebar weight in heavily reinforced beams. The fifth is using nominal diameter when the actual rolling size is slightly larger; mill tolerance is typically ±2%, but most takeoffs use nominal sizes. The sixth is ignoring the difference between deformed rebar (the normal structural type) and plain round bar (used only for ties, hooks, and some non-structural applications); their unit weights are essentially identical. The seventh is forgetting that mesh reinforcement (welded wire fabric, BRC) is sold by weight per m² of mesh, not by linear metre of bar; use mesh-specific tables.
When should I not use this calculator?
Skip it for non-steel reinforcement: GFRP (glass-fibre reinforced polymer) bars have densities of ~2,000 kg/m³ — about 25% of steel — so the d²/162 formula overestimates by 4×. Use manufacturer-supplied unit weights. Avoid it for pre-stressing tendons (7-wire strands), which have specific weights per strand from manufacturer datasheets (typical 12.7 mm strand ≈ 0.775 kg/m, 15.2 mm strand ≈ 1.115 kg/m); the d²/162 formula doesn't apply to bundled multi-wire strands. It is the wrong tool for mesh reinforcement (welded wire fabric), which is sold by area weight (kg/m² of mesh) rather than per-bar weight. Do not use it for non-circular cross-sections (square bars, hollow bars, deformed special sections) where the area is not π·d²/4. And for procurement and supplier orders on large projects, use the supplier's specific weight tables for the rebar grade and rolling tolerance they supply — small differences accumulated over tonnes of steel can translate to significant cost differences.