Rebar calculator: how much rebar do I need?
16 sticks
23 bars: 8 of 20 ft and 15 of 10 ft · 310 linear ft · 207.1 lb of #4 at 0.668 lb/ft · for a 20 × 10 ft grid at 18 in on center
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Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
16 sticks
23 bars: 8 of 20 ft and 15 of 10 ft · 310 linear ft · 207.1 lb of #4 at 0.668 lb/ft
Source: Caltrans Bridge Design Details, Table 13.1.1, ASTM Standard Reinforcing Bar Data (September 2025), weight per foot of each bar size, read October 14, 2026. Data sheet (PDF)
A 10 by 20 ft slab grid with bars at 18 inches on center both ways takes 23 bars and 310 linear feet, which is 16 sticks of 20 ft #4 rebar weighing 207.1 lb, at 0.668 lb per foot.
A worked example
An 18 by 9 1/2 ft grid at 12 in on center in #3 bar, cut from 20 ft sticks, needs 21 sticks. That is 11 bars of 18 ft and 19 bars of 9.5 ft, 378.5 linear feet. Each 18 ft bar takes a stick of its own, two 9.5 ft bars come out of each stick, and at 0.376 lb per foot the order weighs 142.3 lb.
How much does rebar weigh per foot?
A #3 bar weighs 0.376 lb per foot, a #4 0.668 lb and a #5 1.043 lb, from the ASTM bar data printed in Caltrans Bridge Design Details Table 13.1.1. A 20 ft stick of #4 therefore weighs 13.36 lb. Some websites give #4 as 0.688 lb per foot, which is a typo for 0.668. The full table, from #3 to #18, is below.
What else it is called
Rebar is short for reinforcing bar, also called reinforcing steel or deformed bar. It is sold by the stick, and by weight for big orders, which is why the answer gives sticks first and pounds beside them. Up to #8 the size number is the nominal diameter in eighths of an inch: #3 is 3/8 in, #4 is 1/2 in, #5 is 5/8 in.
Rebar sizes and weights
| Bar size | Nominal diameter | Area | Weight per foot | Weight of a 20 ft stick |
|---|---|---|---|---|
| #3 | 0.375 in | 0.11 sq in | 0.376 lb | 7.52 lb |
| #4 | 0.500 in | 0.20 sq in | 0.668 lb | 13.36 lb |
| #5 | 0.625 in | 0.31 sq in | 1.043 lb | 20.86 lb |
| #6 | 0.750 in | 0.44 sq in | 1.502 lb | 30.04 lb |
| #7 | 0.875 in | 0.60 sq in | 2.044 lb | 40.88 lb |
| #8 | 1.000 in | 0.79 sq in | 2.670 lb | 53.40 lb |
| #9 | 1.128 in | 1.00 sq in | 3.400 lb | 68.00 lb |
| #10 | 1.270 in | 1.27 sq in | 4.303 lb | 86.06 lb |
| #11 | 1.410 in | 1.56 sq in | 5.313 lb | 106.26 lb |
| #14 | 1.693 in | 2.25 sq in | 7.650 lb | 153.00 lb |
| #18 | 2.257 in | 4.00 sq in | 13.600 lb | 272.00 lb |
ASTM standard reinforcing bar data as printed in Caltrans Bridge Design Details, Table 13.1.1 (September 2025). The 20 ft stick is 20 times the weight per foot.
Where the numbers come from
- Bars are counted both ways at the spacing you enter, one more than the spaces in each direction, and cut from the stick length you buy. Linear feet is each bar times its length.
- Weight per foot and nominal diameter: Caltrans Bridge Design Details, Table 13.1.1, ASTM Standard Reinforcing Bar Data, September 2025, for #3 to #18 bars: #3 0.376, #4 0.668, #5 1.043 lb per foot. Read October 14, 2026. Caltrans Table 13.1.1 (PDF)
Enter the grid, not the slab: the slab size less the concrete cover you keep at each edge. Bar size and spacing come from your plans or your building department, and this page does not recommend them. A bar longer than a stick is counted end to end with no lap splice added, so add the lap length your plans call for.
By Javier Miralles · Last updated . How this site is made.
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