What the bar number actually says
Rebar is named by a number that, for the common sizes, is just its diameter in eighths of an inch. A #4 bar is 4/8 inch — half an inch across, a #5 is 5/8 inch, and a #8 is a full inch. That rule holds from #3 up to #8. Above #8 it stops: #9, #10, #11, #14 and #18 were sized long ago to match the cross-sectional area of the square bars they replaced, so their diameters (1.128 in, 1.270 in, 1.410 in) look irregular beside the smaller sizes. It is also why there is no #12, #13, #15, #16 or #17 — those square sizes never existed.
Every size has a fixed weight per foot, published by the mill and fixed by ASTM A615. The weight does not depend on the grade: a #4 bar weighs 0.668 lb per foot whether it is Grade 40, Grade 60 or Grade 75, because the grade changes the steel’s strength, not its size. That weight per foot is the single number this calculator multiplies by your total length.
The unit-weight formula
Steel has a density of about 490 lb per cubic foot (0.2836 lb per cubic inch). Multiply a bar’s cross-sectional area by 12 inches and by that density and you have its weight per foot. For a round bar of nominal diameter d inches the area is π d² ÷ 4, which collapses to one easy field formula:
weight (lb/ft) = d² × 2.67
Check it on a #4: d = 0.500 in, so 0.500² × 2.67 = 0.6675, which rounds to the published 0.668 lb/ft. The same quantity written from the other direction is area × 3.40 — 0.196 in² × 12 × 0.2836 = 0.668 lb/ft — and that is the form the size table below uses.
Because the weight scales with the square of the diameter, a bar twice as wide weighs about four times as much per foot: a #8 is 2.670 lb/ft against the #4’s 0.668. Holding that one fact in your head is most of what matters when you are estimating steel by eye.
Standard bar sizes, diameters and weights
| Bar size | Diameter (in) | Area (in²) | Weight (lb/ft) | Typical use |
|---|---|---|---|---|
| #3 | 0.375 | 0.11 | 0.376 | Stirrups, ties, slabs on grade |
| #4 | 0.500 | 0.20 | 0.668 | Slabs, sidewalks, light walls |
| #5 | 0.625 | 0.31 | 1.043 | Footings, walls, driveways |
| #6 | 0.750 | 0.44 | 1.502 | Foundation walls, columns |
| #7 | 0.875 | 0.60 | 2.044 | Beams, heavy footings |
| #8 | 1.000 | 0.79 | 2.670 | Columns, transfer beams |
| #9 | 1.128 | 1.00 | 3.400 | High-rise columns |
| #10 | 1.270 | 1.27 | 4.303 | Heavy columns, bridge piers |
| #11 | 1.410 | 1.56 | 5.313 | Bridge and high-rise work |
| #14 | 1.693 | 2.25 | 7.650 | Heavy structural columns |
| #18 | 2.257 | 4.00 | 13.600 | Major structural elements |
Two things to read carefully. There is no #2 in this table: the #2 bar is made only as a plain, undeformed bar and is not part of the standard deformed series. And the diameter shown is the nominal diameter — that of a plain round bar of the same weight — not the reading you get from calipers across the deformations, which stand roughly 0.05 in proud of the surface.
If you are laying out a grid or a slab, work out the total length first — the rebar material calculator turns spacing into linear feet — then come back here to turn that length into weight.
Worked example 1 — 500 ft of #4
A residential slab takes 500 linear feet of #4. Enter #4 and 500 and the calculator returns 334 lb of #4 rebar. The arithmetic is 500 ft × 0.668 lb/ft = 334 lb, which is 0.17 short tons — 25 standard 20-foot bars. Because a yard usually sells #4 by the ton or by the 20-ft length, both the weight and the piece count matter.
Worked example 2 — 240 ft of #5
A strip footing takes 240 linear feet of #5. Enter #5 and 240 and the result is 250.3 lb. That is 240 × 1.043 = 250.3 lb = 0.13 short tons, or 12 bars at 20 ft. The heavier bar does the same job with far fewer pieces — 12 bars here against 25 for the #4 example — which is why larger bars cut laying time even when the tonnage is similar.
Worked example 3 — 1,200 ft of #3
Stirrups and column ties add up quickly in feet. Enter #3 and 1,200 and you get 451.2 lb: 1,200 × 0.376 = 451.2 lb = 0.23 short tons = 60 bars at 20 ft. Small bars are light per foot, but there are usually far more feet of them, which is why ties are ordered by count rather than by the tonne.
| Example | Bar | Length | Weight | Short tons | 20-ft bars |
|---|---|---|---|---|---|
| Slab | #4 | 500 ft | 334 lb | 0.17 | 25 |
| Footing | #5 | 240 ft | 250.3 lb | 0.13 | 12 |
| Ties | #3 | 1,200 ft | 451.2 lb | 0.23 | 60 |
From feet to bars, bundles and tons
Mills ship standard 20-foot bars (40 ft is also made). To turn a length into pieces, divide by 20: 500 ft is 25 bars, 240 ft is 12. Suppliers also quote steel by weight — a short ton is 2,000 lb — so it helps to know how many feet of each bar make a ton:
| Bar | Weight (lb/ft) | Feet per short ton | 20-ft bars per ton |
|---|---|---|---|
| #3 | 0.376 | 5,319 ft | 266 |
| #4 | 0.668 | 2,994 ft | 150 |
| #7 | 2.044 | 978 ft | 49 |
| #8 | 2.670 | 749 ft | 37 |
Mill bundles hold a fixed number of bars, and the count falls as the bar gets heavier — a #4 bundle is 152 bars, a #18 bundle only 6 — because the bundle is limited by weight, not by count. That is why the price per bar climbs faster than the weight per foot: you are buying the handling as much as the steel.
What the estimate leaves out
- Laps and splices. Bars are overlapped where they join, and every lap spends length that carries no extra steel. A common Class B lap runs 30 to 40 bar diameters, so a #4 lap is roughly 1 to 2 feet; multiply that by the number of splices and add it.
- Waste and cut-offs. Add about 5% for a straightforward layout and up to 10% where bars must be cut around openings.
- Chairs, ties and wire. Bar supports, tie wire and chairs are bought separately and are not counted in this weight.
- Coating. Epoxy or galvanised bars weigh marginally more per foot, but the difference is small enough to ignore when estimating.
Why the weight matters
Weight, not length, is what the truck carries and what the mill bills. Suppliers price small orders by the pound and bulk orders by the ton, and a delivery that quietly exceeds a load rating is a problem you discover on the road. The tonnage also tells you whether a job is a one-person pickup or a flatbed. If you have already sized the concrete with the concrete calculator, the steel weight and the concrete weight together give the real load on the ground and on the vehicle.
Sources and standards
Where these figures come from
The unit weights and nominal diameters on this page follow ASTM A615/A615M Table 1 and the CRSI bar-size tables, and every quantity above was produced by running this calculator on the stated length. Where a value depends on a project’s structural design, it should come from an engineer’s schedule, not from a rule of thumb.
- Concrete Reinforcing Steel Institute (CRSI) (checked 9 Oct 2026) — the US bar-size, area and weight tables in the Manual of Standard Practice.
- ASTM A615/A615M — Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement (checked 9 Oct 2026) — Table 1 defines each bar’s nominal diameter, area and weight per foot.
- Cascade Steel Rolling Mills — Reinforcing Bar (checked 9 Oct 2026) — manufacturer ship weight (lb/ft) and bars per bundle by size.
- ASTM International (checked 9 Oct 2026) — the standards body that publishes the bar specification behind this table.
Figures, formulas and reference tables last checked: 9 October 2026.