Rebar Calculator
Rebar Calculator
Rebar (reinforcing bar) gives concrete its tensile strength, and knowing how much you need — by weight and length — is essential for ordering and budgeting. Our Rebar Calculator estimates the total weight of rebar from the bar size, the length of each bar, and the number of bars. It uses standard US rebar weights per foot, so you can quickly total a slab, footing, or wall without a weight chart.
What Is Rebar?
Rebar is a steel bar with surface ridges (deformations) that bond to concrete. It is sized by a "#" number in the US; a #4 bar is 1/2 inch in diameter and weighs about 0.668 lb per foot. Larger numbers mean thicker, heavier bars.
Why Estimate Weight?
Rebar is sold by weight (often in 20-ft or 60-ft lengths, or by the ton), so a weight estimate lets you price an order and check delivery limits. Length totals help you plan cuts and lap splices.
How bar sizes map to diameter
The "#" number is not the diameter in inches, but for bars #3 through #8 it equals the diameter in eighths of an inch (a #4 is 4/8 = 1/2 in). Above #8 the rule loosens: a #9 is 9/16 in, a #10 is 5/8 in, and an #11 is 11/16 in. Weight per foot scales with cross-sectional area, which is why a #8 (1.0 in) is roughly four times heavier per foot than a #4 (0.5 in), not twice.
- Select the Rebar Size from the dropdown (#3 through #11).
- Enter the Length per Bar in feet.
- Enter the Number of Bars (default 1).
- Click Calculate for total weight in pounds and kilograms and total length.
Worked Example 1: Ten #4 Bars, 20 ft Each
#4 weighs 0.668 lb/ft. Total length = 20 × 10 = 200 ft. Weight = 200 × 0.668 = 133.6 lb (about 60.6 kg).
Worked Example 2: A Single #8 Bar, 40 ft
#8 weighs 2.670 lb/ft. Weight = 40 × 2.670 = 106.8 lb (about 48.4 kg).
Edge Cases
- Zero length → no result.
- Quantity 1 default if left blank.
- Larger bar sizes scale weight roughly with cross-sectional area.
- Metric projects: the calculator reports kilograms alongside pounds.
- Overlapping/lap splices are not added; add extra length if your design laps bars.
Worked Example 3: A Slab With a Grid of #5 Bars
A 20 ft × 30 ft slab on 12 in centers needs bars in both directions. One direction: 21 bars at 30 ft = 630 ft. The other: 31 bars at 20 ft = 620 ft. Total 1,250 ft of #5 (1.043 lb/ft) = 1,304 lb, about 0.65 ton. Add lap and 10% cutting waste and you are near 1.43 ton.
Worked Example 4: Lap Splices on a Tall Wall
A vertical wall needs #6 bars 12 ft long, but stock is 20 ft and bars must lap 40 × diameter = 40 × 0.75 = 30 in (2.5 ft). Each bar then needs 12 + 2.5 = 14.5 ft of stock. Ten bars = 145 ft × 1.502 lb/ft = 218 lb. Forgetting the lap would short the order by about 37 lb.
Mixing sizes in one job
Footings often use lighter bars (#4) while columns use heavy ones (#8 or #9). Estimate each size separately and sum the weights; a single blended number hides which bar to order and how many of each.
Worked Example 5: A Continuous Footing Grid
A 40 ft × 24 ft footing calls for #4 bars at 12 in centers in each direction. One direction: 25 bars × 40 ft = 1,000 ft. The other: 41 bars × 24 ft = 984 ft. Total = 1,984 ft of #4 (0.668 lb/ft) = 1,325 lb, about 0.66 ton. Add 7% cut waste and a 2 ft lap at every splice and you are near 1,450 lb, or roughly 0.73 ton.
Worked Example 6: Columns With Heavy Bars
Four columns each need four #8 bars, 14 ft long, with a 2.5 ft lap splice at the base. Per bar: 14 + 2.5 = 16.5 ft. Per column: 4 × 16.5 = 66 ft. Total: 4 × 66 = 264 ft of #8 (2.670 lb/ft) = 705 lb. The lap splice adds about 107 lb over a no-lap count of 598 lb — a 18% increase you would miss by measuring the clear height only.
Weight per foot vs per meter
A #5 bar is 1.043 lb/ft, which is 1.552 kg/m. Multiply any lb/ft figure by 1.488 to get kg/m, or by 0.453592 then divide by 3.281 to convert the whole length to kilograms. The calculator does this for you, but knowing the per-meter figure helps when a structural schedule lists metric requirements.
Estimating by the ton
For large jobs, convert pounds to tons early. A truckload of #4 (66.8 lb per 5-bar bundle) needs about 30 bundles to reach a ton; a truckload of #8 needs only about 7.5 bundles per ton. The same tonnage is far fewer physical bars for heavy sizes, which changes how you stage deliveries on a tight site.
Each bar size has a standard weight per foot w (lb/ft). Total weight is:
where n is the number of bars, L is the length per bar in feet, and w is the weight per foot for the selected size. To convert to kilograms:
Standard US weights per foot: #3 = 0.376, #4 = 0.668, #5 = 1.043, #6 = 1.502, #7 = 2.044, #8 = 2.670, #9 = 3.400, #10 = 4.303, #11 = 5.313.
Weight per foot for common rebar sizes:
| Bar Size | Diameter (in) | Weight (lb/ft) | Weight (kg/m) |
|---|---|---|---|
| #3 | 0.375 | 0.376 | 0.560 |
| #4 | 0.500 | 0.668 | 0.994 |
| #5 | 0.625 | 1.043 | 1.552 |
| #6 | 0.750 | 1.502 | 2.236 |
| #8 | 1.000 | 2.670 | 3.974 |
Weight grows with the square of diameter, so a #8 is roughly seven times heavier per foot than a #3.
Total weight for 500 ft of rebar at various sizes (lb):
| Bar Size | Weight for 500 ft (lb) |
|---|---|
| #3 | 188 |
| #4 | 334 |
| #5 | 522 |
| #6 | 751 |
| #8 | 1335 |
| #9 | 1700 |
A single size jump can add hundreds of pounds across a long run.
Total weight for 100 ft of rebar at various sizes:
| Bar Size | Weight for 100 ft (lb) |
|---|---|
| #3 | 37.6 |
| #4 | 66.8 |
| #5 | 104.3 |
| #6 | 150.2 |
| #8 | 267.0 |
Because weight is linear in length, doubling the length doubles the total weight for a given size.
Number of #4 bars (20 ft each) for a target weight:
| Total Weight (lb) | Number of Bars |
|---|---|
| 66.8 | 5 |
| 133.6 | 10 |
| 267.2 | 20 |
| 534.4 | 40 |
| 801.6 | 60 |
Each 20 ft #4 bar weighs 13.36 lb, so divide your target weight by that to find the bar count.
- Confirm bar size with your structural drawing; do not guess.
- Add lap splice length: if bars are spliced, add the lap (often 40× diameter) to the per-bar length.
- Order 5-10% extra for cuts and errors.
- Check delivery weight: a full truckload of #8 adds up fast.
- Use kg for metric specs: the calculator shows both units.
- Round lengths to available stock (20 ft, 40 ft, 60 ft) to minimize waste.
- Standard US sizes only: metric bar sizes (e.g., 10M, 15M) are not in the dropdown.
- No lap or overlap: add splice length manually if required.
- Weight is nominal: actual mill weights vary slightly.
- Straight bars only: bent or shaped bars use the same linear weight but may need extra.
- No wastage: add a margin for cutting and mistakes.
- US units: length in feet; weight in lb and kg.
How much does a #4 rebar weigh per foot?
About 0.668 lb per foot (roughly 0.994 kg per meter).
How do I calculate total rebar weight?
Multiply the number of bars by the length per bar and by the weight per foot for that bar size.
What size rebar is 1/2 inch?
A #4 bar is 1/2 inch (0.500 in) in diameter.
How many pounds in a ton of rebar?
2000 lb. Divide your total weight by 2000 to estimate tons.
Does rebar come in standard lengths?
Yes — commonly 20 ft, 40 ft, and 60 ft in the US. Plan cuts around these.
How much extra should I order?
Typically 5-10% for cuts, splicing, and errors.
Can I get weight in kilograms?
Yes, the calculator reports kilograms alongside pounds.
What is rebar used for?
It reinforces concrete in slabs, footings, walls, and columns, providing tensile strength.
Is #8 rebar much heavier than #4?
Yes — about four times the weight per foot (2.670 vs 0.668 lb/ft).
Do I need to add lap splice length?
If your design laps bars, add the splice length (often 40× the diameter) to each bar before estimating.
How do I convert pounds to tons for delivery?
Divide total pounds by 2,000. A 1,335 lb order of #8 is about 0.67 ton; a full 60-ft truckload of #8 can exceed a ton per bundle, so check bundle weights against your vehicle or crane.
What is the difference between epoxy and black rebar?
Same weight, different coating. Epoxy-coated and galvanized bars resist corrosion in wet or coastal exposure but cost more; the weight math is identical, so this calculator applies to either.
Can I estimate a slab mesh with this?
Welded wire mesh is sold by the sheet, not by linear weight, so estimate it by area. Use this tool for straight deformed bars only.
How much does a bundle of rebar weigh?
A common bundle is 5 bars of 20 ft. For #4 that is 5 × 20 × 0.668 = 66.8 lb; for #8 it is 5 × 20 × 2.670 = 267 lb. Bundles make handling and counting easier than loose bars.
What is a development length and does it add weight?
Development (embedment) length is how far a bar must extend into concrete to transfer its force. It is part of the bar length you order, not extra weight, but forgetting it shortens bars. Add the development length to every bar that terminates in a footing or wall.
How do I estimate stirrups and ties?
Stirrups (in beams) and ties (in columns) are bent bars counted separately. Estimate them by the number of spaces along the member times the per-piece length, then apply the same per-foot weight for their bar size (often #3 or #4). They are not part of the straight-bar total this tool returns.
Can I mix metric and US sizes in one schedule?
Not directly. This calculator uses US "#" sizes; metric schedules use designations like 10M, 15M, 20M. Convert each metric bar to its US equivalent (a 15M is close to a #5) or use a metric weight table before summing, so the total tonnage is consistent.
Last updated: July 18, 2026
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