Reinforcement Steel Calculator: Complete Guide
This reinforcement steel calculator helps you figure the weight, length, and cost of rebar for concrete construction. Enter your rebar size, length, and quantity — get results in pounds, total length, and cost.
⚙️ Quick Formula:
Weight = Quantity × Length × Weight per ft
Weight per ft = (Diameter in inches)² × 0.7854 × 0.283 × 12
Example: 10 bars of #4 (1/2") rebar, 20ft each
Weight per ft = 0.668 lbs/ft
Total Weight = 10 × 20 × 0.668 = 133.6 lbs
Understanding Rebar Sizes
Rebar (reinforcement steel) is sized by number, which corresponds to the diameter in 1/8 inch increments:
- #3: 3/8" diameter — light applications
- #4: 1/2" diameter — residential slabs, footings
- #5: 5/8" diameter — commercial slabs, beams
- #6: 3/4" diameter — columns, heavy structures
- #8: 1" diameter — bridges, heavy commercial
- #10: 1-1/4" diameter — heavy industrial, dams
Rebar Weight per Foot Table
- #3: 0.376 lbs/ft
- #4: 0.668 lbs/ft
- #5: 1.043 lbs/ft
- #6: 1.502 lbs/ft
- #7: 2.044 lbs/ft
- #8: 2.670 lbs/ft
- #9: 3.400 lbs/ft
- #10: 4.303 lbs/ft
- #11: 5.313 lbs/ft
Real-World Rebar Examples
- Slab (20' × 30' with #4 @ 16" spacing): ~200 bars × 20ft = 2,672 lbs
- Footing (10' × 10' with #5): ~12 bars × 10ft = 125 lbs
- Column (12ft tall with #6 vertical bars): 4 bars × 12ft × 1.502 = 72 lbs
- Retaining wall (50ft long with #4 horizontal): 50 bars × 20ft = 668 lbs
📋 Real Project: Slab Reinforcement
Project: Concrete slab reinforcement, Austin, TX | Size: 24' × 36' | Rebar: #4 @ 16" spacing
📐 Calculations:
Length direction: 24' ÷ 1.33' = 18 bars × 36' = 648 ft
Width direction: 36' ÷ 1.33' = 27 bars × 24' = 648 ft
Total length: 1,296 ft
Weight: 1,296 × 0.668 = 866 lbs
Cost @ $0.60/lb: 866 × $0.60 = $520
Add 10% waste: 953 lbs → $572
5 Common Rebar Calculation Mistakes
- Using the wrong weight per foot: Different sizes have different weights — check the size.
- Forgetting to add waste: Add 5-10% for laps, splices, and cutting waste.
- Not accounting for laps: Rebar laps add extra length — typically 40-50 times the diameter.
- Mixing imperial and metric: Keep all measurements in feet or inches.
- Ignoring spacing requirements: Check code for minimum and maximum spacing.
🔧 Rebar Troubleshooting
Common rebar estimation problems and solutions.
❌ "My rebar order was too short"
→ You likely forgot to add waste or account for laps. Always add 10% extra for rebar projects.
❌ "The rebar is heavier than expected"
→ Check the rebar size. #5 is much heavier than #4. Use the correct weight per foot for your size.
❌ "My rebar cost is higher than expected"
→ Rebar prices vary by region and size. Get multiple quotes from suppliers. Larger sizes cost more per pound.
Frequently Asked Questions
How do I calculate rebar weight?➕
Weight = Number of bars × Length × Weight per foot. For #4 rebar, weight per foot is 0.668 lbs/ft. Example: 10 bars × 20ft × 0.668 = 133.6 lbs.
What is the weight of #4 rebar per foot?➕
#4 rebar (1/2" diameter) weighs 0.668 pounds per foot. A 20ft stick weighs 13.36 lbs.
How much rebar do I need for a slab?➕
Determine spacing, then calculate number of bars in each direction. For a 20' × 30' slab with #4 @ 16" spacing: ~45 bars × 20ft = 900 ft of rebar.
What is the lap length for rebar?➕
Lap length is typically 40-50 times the bar diameter. For #4 (1/2"), lap is about 20-25 inches. Check local building codes for requirements.
How much does rebar cost per pound?➕
Rebar typically costs $0.50-$0.80 per pound, depending on size and region. Larger sizes and higher grades cost more.
