How to Calculate Rebar Weight

To calculate rebar weight, use one of three proven methods: (1) the volume × density formula — multiply the cross-sectional area by the bar length to get volume, then multiply by the density of steel (490 lb/ft³ or 7850 kg/m³); (2) the unit weight lookup method — read the weight per foot or per meter from a standard rebar weight table and multiply by the total length; (3) the area × length method — multiply the cross-sectional area in square inches by the length in feet and by 3.4 lb/in³ (which is the density of steel in those units). The second method (unit weight lookup) is by far the fastest for on-site work since all you need is the bar size and total length.

To calculate rebar weight in kg, multiply the total bar length in meters by the weight per meter for that bar size. For example, #4 rebar has a weight of 0.994 kg/m. If you have 50 meters of #4, the total weight is 50 × 0.994 = 49.7 kg. If you only have the length in feet, first convert to meters (1 ft = 0.3048 m), then multiply by the kg/m value. The complete kg/m lookup table for all sizes (#2 through #18) is provided in the comparison matrix below.

To calculate the weight of rebar from the bar number (size), you need two pieces of information: the bar size and the total length. Each bar size has a known weight per foot (lb/ft) and weight per meter (kg/m) based on its nominal diameter. For example, #6 rebar weighs 1.502 lb/ft. If you have 100 feet of #6, the weight is 100 × 1.502 = 150.2 lb. To convert to tons, divide by 2000 (150.2 ÷ 2000 = 0.075 tons). The complete lookup table in this guide lists lb/ft and kg/m for every size from #2 to #18.

To calculate weight of rebar in tons, first determine the total weight in pounds, then divide by 2000 (since 1 short ton = 2000 lb). For example, if you have 500 feet of #4 rebar at 0.668 lb/ft, the total weight in pounds is 500 × 0.668 = 334 lb. In tons: 334 ÷ 2000 = 0.167 tons. For larger orders, it's common to express rebar weight in tons when purchasing from steel suppliers. For metric tons (1,000 kg), divide the weight in kg by 1000 instead.

Steel rebar weight per meter is derived from the bar's cross-sectional area and the density of steel (7850 kg/m³). The formula is: weight per meter (kg/m) = (π × d²/4) × 7850, where d is the diameter in meters. For example, #4 rebar has a 12.7 mm (0.0127 m) diameter: area = π × (0.0127)²/4 ≈ 0.0001267 m², weight/m = 0.0001267 × 7850 ≈ 0.994 kg/m. In practice, you don't need to recalculate this — the industry-standard values for all sizes are tabulated in the comparison matrix on this page.

To calculate rebar weight for slab, follow these steps: (1) determine the total bar length in both directions using the slab dimensions, spacing, and edge offset; (2) multiply the total length by the weight per foot (or per meter) for your chosen bar size; (3) add 10–15% for waste, lapping, and offcuts. For example, a 20' × 30' slab with #4 rebar at 12" spacing each way requires approximately 560 feet of rebar total (both directions). At 0.668 lb/ft, that's about 374 lb or 0.187 tons. The interactive calculator on this page handles this automatically once you enter length, width, bar size, and spacing.

To calculate rebar in tons for an entire project, break the work into individual components (slab, footings, walls, beams, columns), calculate the bar length and weight for each, then sum the results. For example: a slab with 374 lb (0.187 tons), footings with 220 lb (0.110 tons), and a wall with 150 lb (0.075 tons) totals 744 lb or 0.372 tons. Add 10–15% for waste, bringing the total to about 0.41–0.43 tons. Steel suppliers typically sell rebar in 20-foot sticks, so you'll also need to calculate the number of pieces based on standard bar lengths.

Tonnage of rebar for a concrete pour is calculated by multiplying the total rebar length by the unit weight, then converting to tons. The formula is: Tonnage = (Total Length × Unit Weight) ÷ 2000 (for short tons) or ÷ 1000 (for metric tons). When estimating for a concrete pour, you should also factor in the reinforcement ratio — typical residential slabs use about 0.5–1.0% steel by volume, while commercial slabs may use 1–2%. This gives you a rough cross-check: if your slab is 10 cubic yards (270 cu ft), the steel weight should be roughly 0.5% of the concrete weight (150 lb/cu ft × 270 cu ft = 40,500 lb concrete, 0.5% = 202 lb of rebar).

To calculate lbs for rebar, simply multiply the total bar length in feet by the weight per foot for that bar size. Formula: Weight (lb) = Length (ft) × Weight per Foot (lb/ft). For example, 300 feet of #5 rebar at 1.043 lb/ft = 300 × 1.043 = 312.9 lb. This is the most common weight calculation for small to medium residential projects where suppliers price by the pound rather than by the ton. Always add 10% minimum for waste when ordering.

To calculate lbs for rebar in a slab: (1) calculate the number of bars in each direction: bars = slab dimension ÷ spacing + 1; (2) multiply by the perpendicular slab dimension to get total length per direction; (3) sum both directions for total length; (4) multiply by lb/ft for your bar size. Example: 25' × 40' slab, #4 @ 12" spacing each way. Direction 1: 40 ÷ 1 + 1 = 41 bars × 25 ft = 1,025 ft. Direction 2: 25 ÷ 1 + 1 = 26 bars × 40 ft = 1,040 ft. Total = 2,065 ft. Weight = 2,065 × 0.668 = 1,379 lb ≈ 0.69 tons.

To calculate pounds of rebar per square foot, divide the total rebar weight in pounds by the slab area in square feet. Formula: Weight per sq ft = Total Weight (lb) ÷ Slab Area (sq ft). For the example above: 1,379 lb ÷ 1,000 sq ft = 1.379 lb/sq ft. This metric is useful for comparing reinforcement density between different designs and for quick estimating. Typical residential slabs range from 0.5 to 2.0 lb/sq ft depending on bar size and spacing. Commercial and industrial slabs often use 2–5 lb/sq ft.

Our interactive rebar weight calculator on this page automatically computes pounds of rebar. Simply enter the slab length, width, bar size, and spacing, and the tool outputs the total length in feet, total weight in pounds, kilograms, and tons — all in real time. You can also use it for single bar runs: enter the bar length and select the size to get an instant weight. For custom layouts, use the manual formula: Weight (lb) = Length (ft) × lb/ft from the reference table.

To convert rebar lf (linear feet) to libras (pounds), multiply the linear footage by the weight per foot for that bar size. The formula is simple: Libras = Linear Feet × Weight per Foot (lb/ft). For example, 120 lf of #6 rebar at 1.502 lb/ft equals 180.24 libras (approximately 180 lb). This conversion is essential when you need to communicate weight to suppliers who price by the pound or when filling out project weight sheets. The per-foot values for all sizes are listed in the comparison matrix below.

The formula to calculate rebar weight for slab combines three steps into a single workflow: (1) Total Length = (⌈L ÷ S⌉ + 1) × W + (⌈W ÷ S⌉ + 1) × L, where L = slab length, W = slab width, S = spacing (all in feet); (2) Gross Weight = Total Length × Unit Weight (lb/ft); (3) Net Weight = Gross Weight × 1.10 (for 10% waste). Or more simply: Weight per sq ft ≈ 2 × Unit Weight ÷ Spacing, which gives you a quick per-square-foot estimate for uniform grids. For #4 @ 12" o.c.: 2 × 0.668 ÷ 1 = 1.336 lb/sq ft. This is useful for ballpark estimates before doing a full takeoff.

The density method for calculating steel rebar weight uses the formula: Weight = Area × Length × Density. For imperial units: Weight (lb) = (π × d²/4 in²) × (Length in ft × 12 in/ft) × (0.284 lb/in³), where d is the diameter in inches and 0.284 lb/in³ is the density of steel. For metric units: Weight (kg) = (π × d²/4 mm²) × (Length in mm) × (0.00000785 kg/mm³). However, this method requires knowing the exact diameter, while the unit weight lookup method (using tabulated lb/ft or kg/m) is faster and more accurate for standard rebar sizes since it accounts for the actual nominal mass per ASTM specifications.

A rebar weight calculator converts bar length into weight instantly: you enter the bar size and the total length (or a full slab layout with dimensions and spacing), and the tool returns the weight in pounds, kilograms, and tons in one step. Names like steel rebar weight calculator, weight of rebar calculator, rebar pound calculator, rebar ton calculator, and rebar tonnage calculator all describe the same tool — the differences are only in the output unit. The interactive rebar weight calculator on this page is built on the ASTM A615 unit-weight table for sizes #2 through #18, so its results match a manual unit-weight lookup exactly. For ordering, remember to add a 10–15% waste allowance on top of the calculator output.

A metric rebar weight calculator multiplies the total length in meters by the weight per meter (kg/m) for the bar size — for example, 45 m of a 12 mm metric bar at 0.888 kg/m = 39.96 kg. The kg/m value comes from the metric unit-weight formula: kg/m = d² ÷ 162, where d is the nominal diameter in millimeters. A rebar weight kg per meter calculator simply automates that multiplication across sizes; a rebar metric weight calculator does the same and usually adds tonnage (kg ÷ 1,000) and total cost per kg. The full kg/m table for US sizes #2–#18 is in the comparison matrix above, and metric-bar (mm-sized) values are in the metric and UK section below.

UK rebar follows BS 4449 / BS 8666 and is specified in metric sizes from H8 to H40 (the H prefix replaces the US # system). Each size has a fixed weight per meter: H8 = 0.395 kg/m, H10 = 0.617 kg/m, H12 = 0.888 kg/m, H16 = 1.579 kg/m, H20 = 2.466 kg/m, H25 = 3.854 kg/m, H32 = 6.313 kg/m, and H40 = 9.864 kg/m. To calculate the weight, multiply the total length in meters by the kg/m value — for example, 120 m of H16 = 120 × 1.579 = 189.5 kg, or 0.19 metric tonnes. Note that UK H-sizes and US #-sizes are close but not identical: H12 (12 mm) is slightly heavier than the #4 (12.7 mm nominal, 0.994 kg/m). For any UK project, always use the H-size kg/m values, not the US table.

A rebar tonnage calculator set to US units converts pounds to short tons by dividing by 2,000: Tons = Total Length (ft) × lb/ft ÷ 2,000. For example, 5,000 ft of #5 rebar at 1.043 lb/ft weighs 5,215 lb = 2.61 US short tons. Keep the ton type straight when comparing quotes: a US short ton is 2,000 lb, while a metric tonne is 2,204.6 lb — roughly 10% heavier, enough to cause a costly purchasing error if the supplier's unit is assumed incorrectly. US suppliers quote short tons; international projects quote metric tonnes. To calculate tons of rebar for a whole project, sum the pound totals of every member first, then divide once — this avoids stacking rounding errors per member.