Rebar Size & Weight Calculator (ASTM A615)

Look up standard rebar sizes or work out the total reinforcement weight for a job in two steps. Pick a bar designation to get its diameter, cross-sectional area and unit weight straight from ASTM A615, or enter bar counts, cut lengths, and hook or lap allowances to get total length, total weight, and a per-size breakdown you can hand straight to a supplier.

Switch between metric (SI) and imperial (US customary) bar designations at the top of the form; every result converts with it.

Units

1 Project & allowances

Set the wastage and rate once — they apply to the whole schedule.

Project / element

Wastage / lap allowance (%)

Typical site allowance is 3–5% for cutting waste, plus laps if not already in the schedule.

Steel rate (per kg)

per kg

Leave 0 to hide the cost figures.

Currency symbol

Add hook / bend allowances per bar

When on, the Hooks column in the schedule adds an allowance to each bar’s cut length (a multiple of the bar diameter).

2 Bar schedule

One row per bar mark. Add as many rows as you need.

Bar bending schedule

#	Member / mark	Bar size	Cut length per bar	No. of bars	Hooks	Unit weight	Eff. length	Total length	Weight	Actions
Total

Quantities are for estimating. Always cross-check against the issued bar bending schedule.

How the calculation works

Bar properties. Nominal diameter, cross-sectional area and mass per unit length are read directly from the ASTM A615 size table for the bar designation(s) you pick (#3–#18, or the metric 10M–55M equivalents).
Cut length. Your entered length is adjusted for standard hook allowances (90° and 180° hooks per ACI 318 development-length provisions) and lap splice length, if you turn those on for a row.
Weight per bar and per size. Cut length × unit weight, multiplied by the quantity for that row, repeated for every row in the table and summed by bar size.
Total weight and total length. Every row is summed to a job total, along with a steel density check (7850 kg/m³) so you can cross-check against a mill certificate.

What to have ready

Bar designation(s) used on the drawings (e.g. #4, #8, or 15M, 25M)
Cut length for each bar mark, or span length if you want the calculator to add development/lap length for you
Quantity of bars for each mark or size
Whether each bar needs a standard hook, and its bend angle

Notes and limitations

Unit weights and dimensions follow ASTM A615/A615M nominal values; actual mill tolerances vary slightly by producer. Hook and lap allowances are simplified defaults — always confirm development and splice lengths against your project’s structural drawings and ACI 318 Chapter 25 for the actual bar size, concrete strength, and cover on your job before ordering.

You can print the takeoff or save it as a PDF from the results panel.

ASTM A615 Rebar Size & Weight Reference Chart

The table below lists all standard ASTM A615 deformed bar designations from #3 through #18. Bar numbers correspond approximately to the bar diameter in eighths of an inch (#4 = 4/8 = 0.500 in). Weight per foot values assume steel density of 490 lb/ft³.

Bar #	Nominal Dia. (in)	Area (in²)	Weight (lb/ft)	Weight (kg/m)	Metric Equiv.
#3	0.375	0.11	0.376	0.560	10M
#4	0.500	0.20	0.668	0.994	13M
#5	0.625	0.31	1.043	1.552	16M
#6	0.750	0.44	1.502	2.235	19M
#7	0.875	0.60	2.044	3.042	22M
#8	1.000	0.79	2.670	3.973	25M
#9	1.128	1.00	3.400	5.060	29M
#10	1.270	1.27	4.303	6.404	32M
#11	1.410	1.56	5.313	7.907	36M
#14	1.693	2.25	7.650	11.390	43M
#18	2.257	4.00	13.600	20.240	57M

Source: ASTM A615/A615M. Weights are nominal; actual may vary ±3.5% per specification.

Rebar Size & Weight Calculator FAQ

What is the most common rebar size for a concrete slab?

#4 rebar (½ in diameter, 0.668 lb/ft) placed at 12-inch centres is the standard choice for 4-inch residential slabs-on-grade. #3 rebar suits light-duty flatwork and driveways; #5 is specified wherever heavier loads or longer spans are expected.

How do you calculate the weight of rebar per foot?

The ASTM formula is: lb/ft = 2.67 × d², where d is the nominal diameter in inches. Example — #5 rebar (d = 0.625 in): 2.67 × 0.625² = 2.67 × 0.3906 ≈ 1.043 lb/ft. This matches the published ASTM A615 table value exactly.

What does ASTM A615 specify?

ASTM A615/A615M covers deformed and plain carbon-steel bars for concrete reinforcement. Grade 60 (420 MPa minimum yield) is the most common in North American construction. Grade 40 is used for light applications; Grades 75 and 80 are available for high-strength designs. The standard also controls deformation geometry, chemical composition, and bend test requirements.

What is the cross-sectional area of #8 rebar?

#8 rebar has a nominal diameter of 1.000 inch and a cross-sectional area of 0.79 in². The bar number system in the U.S. sets the nominal diameter as bar number × ⅛ inch, so #8 = 8 × 0.125 = 1.000 in. Knowing the area is essential for calculating tensile force capacity: T = Aₛ × fy, where fy is the yield strength.

Can two #4 bars substitute for one #6 bar?

Approximately, but not directly. Two #4 bars provide 2 × 0.20 = 0.40 in²; one #6 provides 0.44 in² — an 8% shortfall. Beyond area, spacing, development length, and lap splice requirements all change with bar size. Always verify substitutions with a licensed structural engineer, as ACI 318 development-length provisions are diameter-dependent.