rebar calculator

Rebar Calculator – Estimate Rebar Quantity, Length & Weight Instantly

This Rebar Calculator helps you quickly estimate the number of rebars you need for a concrete slab, foundation, driveway, patio, or any reinforced structure. By entering the slab dimensions, spacing, and bar size, the tool automatically calculates:

• Number of vertical bars
• Number of horizontal bars
• Total bars needed
• Total rebar length
• Estimated rebar weight

Whether you’re a contractor, engineer, DIY builder, or homeowner planning a concrete project, this calculator gives accurate and fast material estimates to help you avoid under-ordering or overspending.

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How the Rebar Calculator Works

Rebar layout typically follows a grid pattern. Bars are spaced evenly in both directions to strengthen the concrete.

1. Number of Bars Formula

Spacing is converted from inches to feet:$$\text{Spacing (ft)} = \frac{\text{spacing (in)}}{12}$$Spacing (ft)=12spacing (in)​

Then:$$\text{Vertical Bars} = \left\lfloor \frac{\text{Width}}{\text{Spacing}} \right\rfloor + 1$$Vertical Bars=⌊SpacingWidth​⌋+1 $$\text{Horizontal Bars} = \left\lfloor \frac{\text{Length}}{\text{Spacing}} \right\rfloor + 1$$Horizontal Bars=⌊SpacingLength​⌋+1

2. Total Rebar Length Formula

$$\text{Total Length} = (\text{Vertical Bars} \times \text{Length}) + (\text{Horizontal Bars} \times \text{Width})$$Total Length=(Vertical Bars×Length)+(Horizontal Bars×Width)

3. Rebar Weight Calculation

Each rebar size has a weight per foot:

Example:
#4 bar = 0.376 lb/ft
#5 bar = 0.668 lb/ft$$\text{Total Weight} = \text{Total Length} \times \text{Weight per Foot}$$Total Weight=Total Length×Weight per Foot

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How to Use the Rebar Calculator

1. Enter the slab length (in feet)

This is the long side of the slab.

2. Enter the slab width (in feet)

This is the short side of the slab.

3. Enter the rebar spacing (in inches)

Common spacing values:

• 12 inches
• 16 inches
• 18 inches
• 24 inches

4. Select the rebar size

Choose from #3 to #8 for accurate weight calculations.

5. Click “Calculate Rebar”

The calculator instantly shows:

• Total bars needed
• Total linear feet of rebar
• Estimated weight
• Vertical and horizontal bar count

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Example Rebar Calculations

✔ Example 1: 20 ft × 10 ft slab, 12-inch spacing

Spacing = 12 in → 1 ft

Vertical bars = floor(10 / 1) + 1 = 11
Horizontal bars = floor(20 / 1) + 1 = 21
Total bars = 32

Total length = (11 × 20) + (21 × 10)
Total length = 220 + 210 = 430 ft

Using #4 bar (0.376 lb/ft):
Weight = 430 × 0.376 = 161.68 lbs

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✔ Example 2: 15 ft × 12 ft patio, 18-inch spacing

18 inches = 1.5 ft spacing

Vertical bars = floor(12 / 1.5) + 1 = 9
Horizontal bars = floor(15 / 1.5) + 1 = 11

Total bars = 20

Total length = (9 × 15) + (11 × 12)
= 135 + 132 = 267 ft

Using #5 bar (0.668 lb/ft):
Weight = 267 × 0.668 = 178.45 lbs

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Why Use This Rebar Calculator?

Perfect for:

• Concrete slabs
• Driveways
• Patios
• Footings and foundations
• Walkways
• Construction estimating
• DIY home projects

Benefits:

✔ Fast and accurate estimates
✔ Helps determine bar counts and total weight
✔ Reduces material waste
✔ Ideal for builders, contractors, and homeowners
✔ Optimized for mobile and desktop use

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Frequently Asked Questions (FAQ)

1. What spacing should I use for rebar?

Common spacing: 12, 16, 18, or 24 inches, depending on load and structure.

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2. What rebar size should I choose?

Typical slab sizes:

• #3 or #4 for patios and walkways
• #4 or #5 for slabs and driveways
• #5 to #8 for structural work

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3. Does this tool calculate weight?

Yes, based on the rebar size (lbs per foot).

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4. Can I use this for metric measurements?

This version uses feet and inches, but I can create a metric rebar calculator if needed.

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5. Does slab thickness affect rebar quantity?

Thickness affects rebar placement but not the number of bars in a grid pattern.

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6. How accurate is the calculator?

It follows standard industry spacing and rebar weight formulas.