Loading Calculator...
Please wait a moment
Please wait a moment
Calculate rebar requirements for concrete slabs, footings, and foundation walls. Determine the number of bars, total weight, tie wire, and costs for your concrete reinforcement project.
#4 = 0.5" diameter, 0.668 lb/ft
#4 rebar
Standard lap splice is 40 times the bar diameter. Grid spacing determines bar count in each direction.
Let us know if this calculator was useful
289 people found this calculator helpful
Rebar (reinforcing bar) is steel reinforcement used in concrete construction to increase tensile strength. While concrete is excellent in compression, it's weak in tension. Rebar provides the tensile strength concrete lacks.
Rebar is designated by numbers that represent the bar diameter in eighths of an inch. For example:
Driveways, patios, garage floors, basement floors
Building foundations, column bases, wall footings
Retaining walls, foundation walls, structural walls
Calculate for both directions (length and width for slabs/footings, or vertical and horizontal for walls).
Slab: 20 ft × 15 ft with #4 rebar @ 18" spacing
Length bars = (15×12 ÷ 18) + 1 = 11 bars
Width bars = (20×12 ÷ 18) + 1 = 14 bars
Total bars = 11 + 14 = 25 bars
Linear ft = (11×20) + (14×15) = 430 ft
20 ft bars needed = 430 ÷ 20 = 22 bars
Weight = 430 × 0.668 = 287 lbs
Add lap splice: 40 × 0.5" = 20" = 1.67 ft per bar
Total with splice = 430 + (25 × 1.67) = 472 ft
| Bar Size | Diameter (in) | Weight (lb/ft) | Common Uses |
|---|---|---|---|
| #3 | 3/8" | 0.376 | Small patios, sidewalks, light-duty slabs |
| #4 | 1/2" | 0.668 | Residential slabs, driveways, most common size |
| #5 | 5/8" | 1.043 | Heavy-duty slabs, footings, retaining walls |
| #6 | 3/4" | 1.502 | Foundation walls, structural footings |
| #7 | 7/8" | 2.044 | Commercial construction, heavy structural |
| #8 | 1" | 2.670 | Large commercial, industrial applications |
| Application | Spacing |
|---|---|
| Residential slab | 18" - 24" |
| Heavy-duty slab | 12" - 18" |
| Foundation wall | 12" - 16" |
| Footing | 12" - 18" |
| Retaining wall | 12" |
Rebar must be at least 1 inch clear from other bars and 1.5 times the maximum aggregate size apart. Never place bars closer than 3 inches apart.
For slabs, maximum spacing is typically 18 inches or 3 times the slab thickness, whichever is less. Check local building codes.
When rebar bars meet end-to-end, they must overlap (lap splice) to transfer stress between bars. The standard lap splice length is 40 times the bar diameter.
| Bar Size | Diameter | Lap Splice |
|---|---|---|
| #3 | 3/8" | 15" |
| #4 | 1/2" | 20" |
| #5 | 5/8" | 25" |
| #6 | 3/4" | 30" |
| #7 | 7/8" | 35" |
| #8 | 1" | 40" |
Rebar intersections must be tied with tie wire (16-18 gauge). Use approximately 1 lb of tie wire per 50 ties.
Typical pattern: Tie every other intersection in a checkerboard pattern, or all intersections for critical applications.
Rebar chairs elevate rebar to maintain proper concrete cover. Space chairs approximately 3-4 feet apart in both directions. Use more chairs for heavier rebar sizes.
#4 (1/2") rebar is most common for residential slabs like driveways and patios. Use #5 (5/8") for heavy-duty applications or areas with heavy equipment. For light-duty sidewalks, #3 (3/8") is sufficient.
Standard spacing is 18 inches for residential slabs. Heavy-duty slabs use 12-inch spacing. Maximum spacing should not exceed 18 inches or 3 times the slab thickness. Always check local building codes.
Rebar is thicker (3/8" to 1"+) steel reinforcement for structural strength. Wire mesh (6x6 10/10) is lighter gauge wire in a grid pattern, suitable for crack control in thin slabs. Rebar provides superior tensile strength.
Not necessarily. For slabs, tying every other intersection in a checkerboard pattern is usually sufficient. For walls and footings, tie all or most intersections to prevent movement during concrete pour.
Standard cover is 3 inches for concrete in contact with ground, 2 inches for concrete exposed to weather, and 3/4 to 1.5 inches for interior slabs. Proper cover prevents rust and ensures structural integrity.
Retaining walls typically use vertical rebar at 12-16 inch spacing with horizontal bars at 8-12 inch spacing. The vertical bars should extend into the footing with proper lap splice. Use #4 or #5 rebar depending on wall height.
Epoxy-coated rebar has a green protective coating that prevents corrosion. It's required for slabs exposed to deicing salts (like bridge decks, parking garages) or marine environments. It costs about 40-70% more than standard rebar.
Check out 8 similar construction calculators