A #4 rebar (0.500 in nominal diameter) weighs 0.668 lb/ft, a #5 rebar (0.625 in) weighs 1.043 lb/ft, and a #6 rebar (0.750 in) weighs 1.502 lb/ft, all values pulled from ASTM A615/A615M nominal tables [S5][S1].
These three sizes cover most residential slab, footing, driveway, and light commercial work in the U.S., and the 0.668 / 1.043 / 1.502 lb/ft triplet is the figure estimators and CRSI Manual of Standard Practice users keep on hand for takeoff [S5][S6].
ASTM A615 Nominal Weights for #4, #5, #6
The ASTM A615/A615M nominal weight column is the contract language: #4 = 0.668 lb/ft, #5 = 1.043 lb/ft, #6 = 1.502 lb/ft, derived from the bar number in eighths-of-an-inch (4/8 = 0.500 in, 5/8 = 0.625 in, 6/8 = 0.750 in) at a steel density of 490 lb/ft³ [S5][S3]. Cross-checks against mill stock charts show #4 = 0.668, #5 = 1.043, #6 = 1.502, matching the ASTM column to the third decimal and confirming the table is not vendor-fudged [S1][S4][S6]. The Engineering ToolBox lists the same three bars at 0.67, 1.04, and 1.50 lb/ft (rounded to two decimals), which is the same data presented with a coarser resolution [S2]. For ordering and shipping reconciliation, contractors use the three-decimal ASTM values; for mental math, the rounded pair is fine.
The mill tolerance is the gotcha: ASTM A615 lets a single bar underrun the nominal weight by up to 6%, so a truckload of #5 ordered at 20,860 lb may legally arrive at 19,608 lb or heavier [S5]. That tolerance is why takeoff software multiplies by nominal weight, not theoretical cross-section weight, when computing steel totals.
Per-Stick and Per-Ton Numbers for the Same Three Sizes
Sticks are where the lb/ft number earns its keep: #4 × 20 ft = 13.36 lb per stick, #5 × 20 ft = 20.86 lb, #6 × 20 ft = 30.04 lb, and a ton (2,000 lb) of #4 yields roughly 150 pieces, of #5 about 96 pieces, of #6 about 67 pieces in 20-foot lengths [S3][S6]. Harris Supply's stock chart lists the identical 0.668 / 1.043 / 1.502 lb/ft triplet, and Formtech's Grade 60 chart quotes the 20-foot stick masses as 13.36 lb, 20.86 lb, and 30.04 lb respectively, which is the number a foreman reads off a bundle tag [S4][S6].
For 40-foot deliveries, the same numbers double: 26.72 lb (#4), 41.72 lb (#5), 60.08 lb (#6); for 60-foot, 40.08 lb, 62.58 lb, 90.12 lb, with #5 and larger commonly shipped in 30-, 40-, and 60-foot lengths from the mill [S5]. A bundle of 50 sticks of #4 × 20 ft therefore weighs 668 lb, and a standard 1,500-lb payload pickup can carry about 100 such sticks; this is the loading math estimators run before dispatch [S5].
Soft-Metric Cross-Reference: Where #4, #5, #6 Sit in the CSA System
Canadian CSA G30.18 metric bars are sized by nominal diameter in millimeters rounded to a whole number, so a #4 (0.500 in / 12.7 mm) does not have an exact match; the closest Canadian bar by area is 10M (11.3 mm, 100 mm², 0.528 lb/ft) [S5]. A #5 (15.9 mm, 0.31 in²) maps to 15M (16.0 mm, 200 mm², 1.055 lb/ft), and a #6 (19.1 mm, 0.44 in²) maps to 20M (19.5 mm, 300 mm², 1.582 lb/ft) [S5].
For U.S. projects that bill by hundredweight (cwt), 100 lb of #4 covers 149.7 ft, 100 lb of #5 covers 95.9 ft, 100 lb of #6 covers 66.6 ft, which is the inverse of the lb/ft column and the table purchasing agents actually flip to [S6]. See also the Rebar Pricing: $/cwt vs $/ton vs $/piece comparison for how these weights feed into the dollar side of the takeoff.
What These Three Sizes Get Used For
#4 (0.668 lb/ft) is the slab-and-patio workhorse: 4-in. residential slabs on grade, broom-finished driveways, sidewalks, and small grade beams where the engineer calls out a single mat of #4 at 12 to 18 in. on center [S3]. #5 (1.043 lb/ft) covers footings, foundation walls, and heavier driveways; it is the smallest bar most U.S. codes will accept in a footing running parallel to the wall, and it is also the standard dowel out of a footing into a stem wall [S3][S5]. #6 (1.502 lb/ft) is the first size that shows up in two-way slabs, commercial footings, and retaining-wall mats, where the 50% jump in steel area over #5 (0.44 in² vs 0.31 in²) actually moves the design [S5].
For placement tolerance on these sizes, ACI 117 covers the cover, spacing, and effective-depth numbers the inspector will check; the ACI 117 Rebar Placement Tolerances reference walks through the values that interact with the chosen bar diameter. If the pour is a deep one, poker head length vs concrete layer depth sets the lift depth, and a single layer of #5 (0.994 kg/m, 1.043 lb/ft) at 12 in. on center adds 1.04 psf of steel to the slab, a number worth keeping in the head before the pump truck arrives.
How the lb/ft Numbers Are Calculated (and Where the Common Errors Are)
The theoretical formula is straightforward: weight per foot = (D² × π / 4) × ρ × (1 / 144), with D in inches and ρ = 490 lb/ft³ for steel [S3]. Plugging in for #4 gives (0.500² × 0.7854) × 490 / 144 = 0.668 lb/ft, and the same arithmetic yields 1.043 for #5 and 1.502 for #6, which is why the calculated values and the ASTM nominals agree to the third decimal [S3][S5]. The two ways to get a wrong answer are: (1) using 0.283 lb/in³ (the reciprocal of the wrong density) instead of 490 lb/ft³, which shortchanges the result by 1.6%, and (2) using the bar number as the diameter in inches (i.e., treating #4 as 4 in.), which is the classic estimator error and overshoots the real weight by a factor of 64 [S3].
A subtler source of error is over-reliance on the "lb/ft" number as delivered mass rather than nominal mass. Because the ASTM tolerance lets a bar weigh 6% under nominal, a scale ticket on #5 that reads 20,000 lb is not a short shipment; it is within the spec, and a contractor who billed the client on the nominal 20,860 lb and the supplier on the scale ticket 20,000 lb will see a 4% spread that has to be reconciled against the standard, not against the contract [S5].
Quick Reference: #4, #5, #6 Numbers Engineers Reuse
For estimators and detailers who need the three sizes on one card: #4 = 0.500 in diameter, 0.20 in² area, 0.668 lb/ft, 13.4 lb per 20-ft stick, ~150 pieces per ton, 0.994 kg/m [S1][S3][S5][S6]. #5 = 0.625 in, 0.31 in², 1.043 lb/ft, 20.9 lb per 20-ft stick, ~96 pieces per ton, 1.552 kg/m [S1][S3][S5][S6]. #6 = 0.750 in, 0.44 in², 1.502 lb/ft, 30.0 lb per 20-ft stick, ~67 pieces per ton, 2.235 kg/m [S1][S3][S5][S6]. Grade (40, 60, 75, 80, 100) does not change the lb/ft figure; it changes yield and tensile strength only, so the same weight table applies whether the bar is Grade 60 or Grade 80 [S5].
Two signals worth tracking over the next quarter: any update to ASTM A615/A615M that revises the nominal mass column (rare, but a re-issue would propagate through every takeoff tool) and any movement in the rebar pricing units that shifts whether suppliers quote by cwt, ton, or stick for these three sizes. The lb/ft numbers themselves are stable engineering data and unlikely to change.
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