Rebar Weight Calculator

1. Pick the bar size: a US number from #3 to #18, a Canadian size from 10M to 55M, or a metric diameter from 8 to 32 mm.
2. Enter the length per bar and choose feet or metres.
3. Enter the number of bars of that size and length.
4. Add a waste allowance if you want spare weight for offcuts, then read the total.

Here is what each result line means:

A rebar weight calculator turns a bar size, a length and a count into a weight. Reinforcing steel is sold, shipped and often priced by weight, while drawings list it by size, length and number, so converting between the two is a routine job for estimators, detailers and anyone ordering bar.

Each bar size has a nominal weight per unit length set by its nominal diameter. This tool holds those weights for three common systems and does the multiplication and unit conversion for you. It is built for a list of bars you already know, such as the longitudinal bars in a concrete beam or the verticals in a concrete column. It does not lay out a slab grid; it weighs bars once you know how many there are.

Rebar weight is length times weight per length. The weight per length comes from the bar size, so the only real work is choosing the right unit weight and keeping the units consistent.

1. Look up the nominal unit weight for the bar size: pounds per foot for US sizes, kilograms per metre for metric sizes.
2. Convert the bar length into the matching unit, using 1 foot = 0.3048 metres.
3. Multiply the unit weight by the length per bar, then by the number of bars.
4. Multiply by 1 plus the waste percentage over 100, then convert pounds and kilograms with 1 lb = 0.45359237 kg.

For metric bars, Hong Kong standard CS2:2012 states that steel has a mass of 0.00785 kg per square millimetre per metre run, which is a steel density of 7,850 kg per cubic metre. Nominal mass per metre is the nominal area times 0.00785. The calculator uses that relation for Canadian M bars, taking the area from the nominal diameter, because only the diameters were checked against a primary source for this page.

Suppose a footing schedule calls for 50 #4 bars, each 20 feet long, and you want the bare weight with no waste.

Calculation: a #4 bar has a nominal weight of 0.668 lb/ft. The total length is 50 x 20 = 1,000 ft, or 304.8 m. The weight is 1,000 x 0.668 = 668.0 lb. In kilograms that is 668 x 0.45359237 = 303.0 kg, which is 0.33 short tons or 0.30 tonnes. Each bar weighs 20 x 0.668 = 13.36 lb, shown as 13.4 lb. The unit weight in metric is 0.668 x 1.48816394 = 0.994 kg/m.

The lesson: once you know the weight per foot, the rest is multiplication. Getting the bar size right matters far more than the arithmetic, because one size up adds roughly 20 to 80 percent to the weight per foot (a #5 weighs 1.043 lb/ft against 0.668 for a #4).

US inch-pound bars, from the Caltrans Bridge Design Details table of ASTM standard reinforcing bar data, given for ASTM A706 Grade 60 reinforcement. The kg/m column is converted at 1 lb/ft = 1.48816 kg/m.

Metric bars by diameter, from Hong Kong CS2:2012 Table 2:

Canadian M bars, with nominal diameters from a North American Stainless bar sheet and masses computed here as pi times the diameter squared over 4, times 0.00785. Published CSA nominal masses were not verified for this page and may differ slightly; check your supplier for billing weights.

Bar Diameter

Weight follows the cross-sectional area, which grows with the square of the diameter. A #8 bar is twice the diameter of a #4 but weighs four times as much per foot, 2.670 against 0.668 lb.

Length and Count

Weight rises in a straight line with total length. Twice as many bars, or bars twice as long, means twice the weight.

Laps, Hooks and Bends

Lap splices, hooks and bent ends all add bar length. Weigh the full developed length of each bar, not just the straight run shown on a plan.

Mill Variation

Real bars are rolled to tolerances, so delivered weight can differ a little from nominal. The tool uses nominal weights, which is the usual basis for estimating.

Offcuts and Spares

Cutting bars from stock lengths leaves offcuts. A small waste allowance covers them when you are ordering stock rather than cut-to-length bar.

The three systems name bars differently, but each size still maps to a diameter and a weight per length.

Do not swap sizes across systems by name. A 10M bar is 11.3 mm in diameter, not 10 mm, and a #4 is 12.7 mm, so a substitution needs the engineer to compare areas, not labels.

Ordering and Pricing Bar

Suppliers often quote by weight. Turn the bar list into pounds, kilograms or tons before you ask for a price.

Planning Delivery and Handling

Know the weight of a bundle before it arrives, so you can plan unloading, storage and lifting.

Checking a Takeoff

Compare a quoted or invoiced weight against the bar list for walls such as a concrete wall or a retaining wall.

Converting Between Systems

Express a metric bar list in pounds and short tons, or a US list in kilograms and tonnes.

1. Reading the Bar Number as the Diameter

A #4 bar is half an inch, not four inches, and a 10M bar is not 10 mm. Always pick the size from the list rather than typing a diameter.

2. Mixing Feet and Metres

Entering a metric length with the unit set to feet understates the weight by about a factor of 3.3. Check the length unit before reading the result.

3. Leaving Out Laps and Hooks

Weighing only the straight plan length misses the extra bar in splices and bends. Use the developed length.

4. Confusing Short Tons and Tonnes

A short ton is 2,000 lb; a metric tonne is 1,000 kg, about 2,205 lb. The tool shows both so they are not mixed up.

5. Treating Nominal Weight as the Billed Weight

Nominal weights are for estimating. The supplier’s scale weight or mill figures decide the invoice.

The arithmetic is exact for nominal weights; real bars and real bar lists add small differences.

It depends on the size. Nominal weights are 0.376 lb/ft for #3, 0.668 for #4, 1.043 for #5, 1.502 for #6 and 2.670 for #8, up to 13.600 lb/ft for #18.

Multiply the length of each bar by its nominal weight per foot or per metre, then by the number of bars. Fifty 20 foot #4 bars are 1,000 feet x 0.668 lb/ft = 668 lb.

About 13.4 lb: 20 feet x 0.668 lb/ft = 13.36 lb, or about 6.1 kg.

About 20.9 lb: 20 feet x 1.043 lb/ft = 20.86 lb, or about 9.5 kg.

Hong Kong standard CS2:2012 gives 0.888 kg per metre for a 12 mm bar, with a nominal area of 113.1 square millimetres.

Nominal mass per metre is the nominal cross-sectional area in square millimetres times 0.00785, which corresponds to steel at 7,850 kg per cubic metre. For a 16 mm bar, 201.1 x 0.00785 = 1.579 kg/m.

No. A Canadian 10M bar has a nominal diameter of 11.3 mm, so it is heavier than a 10 mm bar. Pick the size from the matching system.

Weight follows area, and area grows with the square of the diameter. Doubling the diameter, as from #4 to #8, makes the bar about four times as heavy per foot.

Divide 2,000 lb by the weight of one bar. One 20 foot #4 bar weighs 13.36 lb, so a short ton is just under 150 of those bars (149 whole bars).

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Caltrans Bridge Design Details 13.1, reinforcement (California Department of Transportation; ASTM standard reinforcing bar data, #3 to #18).
• Hong Kong CS2:2012, steel reinforcing bars for the reinforcement of concrete (Civil Engineering and Development Department, Hong Kong; metric bar areas and masses).
• North American Stainless reinforcement bars sheet (Manufacturer; Canadian M bar nominal diameters).