Rebar Size Chart: Diameter, Weight & Area (US #3–#18 vs Metric Ø6–Ø40)
Rebar Size Chart: Diameter, Weight & Area (US #3–#18 vs Metric Ø6–Ø40)
Every rebar question on a job site comes down to three numbers: how thick the bar is, what it weighs, and how many you need to order. The trouble is that there are two numbering systems — US bar numbers and metric diameters — and drawings, quotes and delivery tickets mix them freely. This chart puts both side by side, explains where the numbers come from, and shows the one place where "just convert the diameter" goes wrong.
US bar numbers: eighths of an inch
A US bar number is the nominal diameter in eighths of an inch. A #4 is 4/8" = 1/2", a #5 is 5/8", a #8 is a full inch. That holds cleanly up to #8. From #9 upward the sizes were defined as round bars with the same weight as the old square bars (1", 1⅛", 1¼", 1½" and 2" square), which is why a #9 is an odd 1.128" and there is no #12, #13, #15, #16 or #17.
US rebar chart (ASTM A615)
Nominal diameter, weight per foot and cross-section — the values on reinforcement schedules and delivery tickets. Each size links to its full page.
- #3 — 3/8" (9.53 mm) · 0.376 lb/ft (0.560 kg/m) · 0.11 in² (71 mm²) · 20 ft bar 7.5 lb
- #4 — 1/2" (12.70 mm) · 0.668 lb/ft (0.994 kg/m) · 0.20 in² (129 mm²) · 20 ft bar 13.4 lb
- #5 — 5/8" (15.88 mm) · 1.043 lb/ft (1.552 kg/m) · 0.31 in² (200 mm²) · 20 ft bar 20.9 lb
- #6 — 3/4" (19.05 mm) · 1.502 lb/ft (2.235 kg/m) · 0.44 in² (284 mm²) · 20 ft bar 30.0 lb
- #7 — 7/8" (22.23 mm) · 2.044 lb/ft (3.042 kg/m) · 0.60 in² (387 mm²) · 20 ft bar 40.9 lb
- #8 — 1" (25.40 mm) · 2.670 lb/ft (3.973 kg/m) · 0.79 in² (510 mm²) · 20 ft bar 53.4 lb
- #9 — 1.128" (28.65 mm) · 3.400 lb/ft (5.060 kg/m) · 1.00 in² (645 mm²) · 20 ft bar 68.0 lb
- #10 — 1.270" (32.26 mm) · 4.303 lb/ft (6.404 kg/m) · 1.27 in² (819 mm²) · 20 ft bar 86.1 lb
- #11 — 1.410" (35.81 mm) · 5.313 lb/ft (7.907 kg/m) · 1.56 in² (1,006 mm²) · 20 ft bar 106.3 lb
- #14 — 1.693" (43.00 mm) · 7.650 lb/ft (11.38 kg/m) · 2.25 in² (1,452 mm²) · 20 ft bar 153.0 lb
- #18 — 2.257" (57.33 mm) · 13.600 lb/ft (20.24 kg/m) · 4.00 in² (2,581 mm²) · 20 ft bar 272.0 lb
Metric rebar chart (EN 10080, B500)
Nominal weight and cross-section, plus the two numbers every order comes down to: what a 12 m mill bar weighs and how many bars make a tonne.
- Ø6 · 0.222 kg/m · 28.3 mm² · 12 m bar 2.66 kg · 375 bars per tonne
- Ø8 · 0.395 kg/m · 50.3 mm² · 12 m bar 4.74 kg · 210 bars per tonne
- Ø10 · 0.617 kg/m · 78.5 mm² · 12 m bar 7.40 kg · 135 bars per tonne
- Ø12 · 0.888 kg/m · 113 mm² · 12 m bar 10.66 kg · 93 bars per tonne
- Ø14 · 1.21 kg/m · 154 mm² · 12 m bar 14.52 kg · 68 bars per tonne
- Ø16 · 1.58 kg/m · 201 mm² · 12 m bar 18.96 kg · 52 bars per tonne
- Ø20 · 2.47 kg/m · 314 mm² · 12 m bar 29.64 kg · 33 bars per tonne
- Ø25 · 3.85 kg/m · 491 mm² · 12 m bar 46.20 kg · 21 bars per tonne
- Ø28 · 4.83 kg/m · 616 mm² · 12 m bar 57.96 kg · 17 bars per tonne
- Ø32 · 6.31 kg/m · 804 mm² · 12 m bar 75.72 kg · 13 bars per tonne
- Ø40 · 9.86 kg/m · 1,257 mm² · 12 m bar 118.32 kg · 8 bars per tonne
US ↔ metric: nearest sizes, and the trap
Matching by diameter gives these pairs:
- #3 ≈ Ø10 (9.53 vs 10 mm) · #4 ≈ Ø12 (12.70 vs 12) · #5 ≈ Ø16 (15.88 vs 16 — the closest match in the whole chart)
- #6 ≈ Ø20 (19.05 vs 20) · #8 ≈ Ø25 (25.40 vs 25) · #9 ≈ Ø28 (28.65 vs 28)
- #10 ≈ Ø32 (32.26 vs 32) · #14 ≈ Ø40 (43.0 vs 40 — a rough one)
- #7, #11 and #18 have no clean metric partner: #7 (22.2 mm) sits between Ø20 and Ø25, #11 (35.8 mm) between Ø32 and Ø40, and #18 (57.3 mm) is beyond the common metric range.
The trap is that reinforcement is designed by steel area, not by bar count. A #4 has 129 mm² of steel, a Ø12 only 113 mm² — 14% less. Swap five #4 bars for five Ø12 and the section is under-reinforced (565 mm² instead of 645); you need six Ø12 (678 mm²). The #5 ↔ Ø16 pair is the exception where the count survives: 4 × #5 = 800 mm², 4 × Ø16 = 804 mm². Whenever a drawing crosses the Atlantic, convert the required area and re-count the bars.
Where the weights come from
- Metric: kg/m = d² / 162, with d in millimeters. Ø16: 256 / 162 = 1.58 kg/m. The 162 is simply 4 / (π × 7,850 kg/m³) scaled to millimeters.
- US: lb/ft = 2.67 × d², with d in inches — or 3.4 × area in in². #8: 2.67 × 1² = 2.67 lb/ft.
The ribs do not change either number: the nominal diameter is defined as the diameter of a plain round bar with the same mass per length, so a caliper reading over the ribs is always a little more than nominal. Delivered weight may also differ from the chart: EN 10080 allows ±4.5% on mass for Ø8 and above (±6% below), and ASTM A615 allows an individual bar to be up to 6% under nominal. Invoices use nominal weight either way.
From drawing to order: a slab example
A 20 ft × 13 ft slab, #4 bars at 12" on center both ways, 1.5" cover. Along the 20 ft side you need 13 + 1 = 14 bars, each 20 ft − 3" = 19.75 ft; across it, 20 + 1 = 21 bars of 12.75 ft. That is 276.5 + 267.75 = 544 ft of #4 = 364 lb in the slab.
What you buy is a different number, and it depends on stock length:
- 20 ft stock: every 19.75 ft piece takes a whole bar (14 bars), and every 12.75 ft piece also takes a whole bar, leaving a 7.25 ft offcut (21 bars). 35 bars = 700 ft = 468 lb, 22% of it waste.
- 40 ft stock: two 19.75 ft pieces per bar (7 bars) and three 12.75 ft pieces per bar (7 bars). 14 bars = 560 ft = 374 lb, under 3% waste.
Same slab, same steel — 94 lb difference from the stock length alone. Add lap splices wherever a bar is too long for one piece (typically 40–50 bar diameters, per the design) before you order. For more than two cut lengths, the cutting optimizer does this arithmetic and prints the cut list.
Quick answers
- What is the diameter of #5 rebar? 5/8" — 0.625 in or 15.88 mm. It weighs 1.043 lb/ft (1.552 kg/m).
- What is the diameter of #4 rebar? 1/2" — 0.500 in or 12.70 mm; 0.668 lb/ft (0.994 kg/m).
- How much does Ø12 rebar weigh? 0.888 kg/m; a 12 m bar is 10.66 kg and a tonne is 93 bars.
- What is the metric equivalent of #5 rebar? Ø16 — 15.88 vs 16.00 mm, and the areas match too (200 vs 201 mm²).
- How many #4 bars are in a ton? A 20 ft #4 weighs 13.4 lb, so a US ton (2,000 lb) is about 149 bars.
Charts and tools
The full US rebar chart and metric rebar chart list every size with bar weights, tons and tonnes, and the nearest cross-system match. The rebar calculator turns slab dimensions or a bar list into bars, kilograms, lap splices and the stock order with a cutting list. The metal weight calculator handles any diameter and length, and the cutting optimizer turns any other bar schedule into the cheapest stock order.