Rebar Calculator — Concrete-Depot.com

Calculate rebar quantity, bar count, weight, and material cost for slabs, footings, and walls — imperial or metric.

Slab Length ( ft ) Overall slab length Enter a positive number

Slab Width ( ft ) Overall slab width Enter a positive number

Bar Spacing ( in ) Typical: 12 in on centre

Edge Offset ( in ) Gap from edge to first bar

Waste % Allow 10–15% for cuts

Bar Size #4 most common

Layers (mats) Residential = 1

Slab Thickness ( in ) For concrete vol.

Live 3D Preview

How to use this calculator

Choose your project type — select Slab, Footing, or Wall at the top. Use the unit toggle to switch between Imperial (ft/in) and Metric (m/mm).
Enter your dimensions — type in the length, width/height, spacing, bar size, and cover. Results update live as you type.
Review your results — the result box shows total rebar length, bar count, weight, and cost estimate. The 3D preview on the right updates with your dimensions.
Download the PDF report — once results appear, click "Download PDF Report" for a branded printable estimate including the 3D diagram and rebar reference table.

Tips: Always add 10–15% waste for cuts, laps, and corner hooks. Verify spacing requirements with your local building code. Consult a structural engineer for load-bearing applications.

Formulas used

Slab (two-way grid)

Bars in length = floor((length - 2×edge) / spacing) + 1

Bars in width = floor((width - 2×edge) / spacing) + 1

Total length = (bars_len × width) + (bars_wid × length)

Weight (lb) = total_length_ft × weight_per_ft

With waste = total_length × (1 + waste% / 100)

Footing (strip)

Long. length = num_bars × footing_length

Tie perimeter = 2×(width + depth) - 8×cover (U-shape approx.)

Tie count = floor(footing_length / tie_spacing) + 1

Total length = long_length + (tie_count × tie_perimeter)

Wall (two-way grid)

Vert. bars = floor((length - 2×cover) / v_spacing) + 1

Horiz. bars = floor((height - 2×cover) / h_spacing) + 1

Total length = (vert×height + horiz×length) × faces

Weight per foot values per ASTM A615: #3 = 0.376, #4 = 0.668, #5 = 1.043, #6 = 1.502, #7 = 2.044, #8 = 2.670 lb/ft

Rebar dimension chart (#3 – #11)

ASTM A615 standard sizes — US imperial system. Bar number = nominal diameter in eighths of an inch.

Bar #	Diameter (in)	Diameter (mm)	Area (in²)	Wt / ft (lb)	Wt / m (kg)	Common use
#3	0.375	9.5	0.11	0.376	0.560	Patios, driveways
#4	0.500	12.7	0.20	0.668	0.994	Slabs, footings
#5	0.625	15.9	0.31	1.043	1.552	Struct. slabs, walls
#6	0.750	19.1	0.44	1.502	2.235	Retaining walls
#7	0.875	22.2	0.60	2.044	3.042	Beams, columns
#8	1.000	25.4	0.79	2.670	3.973	Heavy structural
#9	1.128	28.7	1.00	3.400	5.060	Large columns
#10	1.270	32.3	1.27	4.303	6.404	Bridges, highways
#11	1.410	35.8	1.56	5.313	7.907	Infrastructure

Source: ASTM A615/A615M Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement.