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Rebar Size Chart
Quick answer: Rebar numbers are eighths of an inch, so #4 = 1/2″ and #5 = 5/8″. Weight in lb/ft is roughly 3.4 × the area in sq in. Standard lap is 40 bar diameters.
Every US rebar size with diameter, weight and area, plus the three numbers inspectors actually check: concrete cover, lap splice length and bar spacing.
Rebar size chart
US rebar is numbered in eighths of an inch. A #4 bar is 4/8″ = 1/2″ diameter. That holds cleanly from #3 to #8; above #8 the numbering follows cross-sectional area instead, which is why a #9 is 1.128″ rather than 1.125″.
| Bar | Diameter (in) | Diameter (mm) | Weight (lb/ft) | Area (sq in) | Weight per 100 ft (lb) |
|---|---|---|---|---|---|
| #3 | 0.375 | 9.5 | 0.376 | 0.11 | 37.60 |
| #4 | 0.500 | 12.7 | 0.668 | 0.20 | 66.80 |
| #5 | 0.625 | 15.9 | 1.043 | 0.31 | 104.30 |
| #6 | 0.750 | 19.1 | 1.502 | 0.44 | 150.20 |
| #7 | 0.875 | 22.2 | 2.044 | 0.60 | 204.40 |
| #8 | 1.000 | 25.4 | 2.670 | 0.79 | 267.00 |
| #9 | 1.128 | 28.7 | 3.400 | 1.00 | 340.00 |
| #10 | 1.270 | 32.3 | 4.303 | 1.27 | 430.30 |
| #11 | 1.410 | 35.8 | 5.313 | 1.56 | 531.30 |
Weights are nominal for deformed billet-steel bars to ASTM A615. The rule of thumb behind the weight column: lb/ft ≈ 3.4 × area in sq in, which holds to within 2% across the whole range.
What each size is for
| Bar | Typical residential use |
|---|---|
| #3 (3/8″) | Slab mesh replacement, driveway and patio grids, light footings, stirrups |
| #4 (1/2″) | The residential default — footings, foundation walls, slabs, block-wall verticals |
| #5 (5/8″) | Heavier footings, retaining walls, garage and driveway slabs carrying vehicles |
| #6 (3/4″) | Structural retaining walls, grade beams, heavy foundations |
| #7 and up | Engineered structures — columns, large beams. Specified by an engineer, not chosen from a chart |
Cover, lap and spacing — the three that get inspected
| Condition | Minimum cover |
|---|---|
| Cast against and permanently exposed to earth | 3″ |
| Exposed to earth or weather, #6 and larger | 2″ |
| Exposed to earth or weather, #5 and smaller | 1-1/2″ |
| Not exposed to weather — slabs and walls | 3/4″ |
Per ACI 318. Your local building department governs, and some jurisdictions require more.
Lap splices where two bars overlap are typically 40 bar diameters for standard residential work — so a #4 bar laps 40 × 0.5″ = 20″, and a #5 laps 25″. Some jurisdictions and mix designs call for more; the engineer’s drawing wins over any rule of thumb.
Spacing is usually specified as a grid, most often 12″ or 18″ on centre in residential slabs. Bars must be at least one bar diameter apart, and at least 1″ clear, so the aggregate can flow between them.
Grades
| Grade | Yield strength | Marking | Use |
|---|---|---|---|
| Grade 40 | 40,000 psi | No line, or the number 4 | Older and light residential work |
| Grade 60 | 60,000 psi | One line, or the number 6 | The standard for almost everything today |
| Grade 75 | 75,000 psi | Two lines, or 75 | Heavy commercial and columns |
Bars are rolled with marks identifying the mill, bar size, steel type and grade. If a drawing calls for Grade 60 and the bar shows no grade line, do not substitute — the yield difference is 50%.
Frequently asked questions
What size is #4 rebar?
1/2 inch (12.7 mm) diameter. US rebar numbers are eighths of an inch, so #4 = 4/8 in. It weighs 0.668 lb per foot and has a cross-sectional area of 0.20 sq in.
How much does rebar weigh per foot?
#3 is 0.376 lb/ft, #4 is 0.668, #5 is 1.043 and #6 is 1.502. The underlying relation is weight in lb/ft ≈ 3.4 × cross-sectional area in square inches.
How far should rebar overlap?
Commonly 40 bar diameters for residential work — 20 in for #4 bar, 25 in for #5. Where an engineer has specified a lap length, that governs; local codes and mix designs can require more.
How much concrete cover does rebar need?
3 in when cast directly against earth, 2 in for #6 and larger exposed to weather, 1-1/2 in for #5 and smaller exposed to weather, and 3/4 in for interior slabs and walls, per ACI 318.