Rebar Calculator

Free online rebar calculator to estimate the number of reinforcement bars needed for concrete slabs, beams, and columns. Calculate rebar quantity, length, and weight based on dimensions and spacing.

The Rebar Calculator helps you estimate the amount of reinforcement steel bars (rebar) needed for concrete construction projects. Enter slab dimensions, rebar size, and spacing to calculate the number of bars, total length, and weight required.

What is a Rebar Calculator?

A Rebar Calculator is an essential construction tool that estimates the quantity of reinforcement steel bars (rebar) needed for concrete structures like slabs, beams, and columns. By entering the dimensions of your concrete element and the desired rebar size and spacing, the calculator determines how many bars you need, their total length, and approximate weight, helping with material ordering and cost estimation.

How to Use the Rebar Calculator

Enter the slab or structure length and width in your preferred unit
Select the rebar size (diameter) - common sizes are #3 (8mm) to #8 (25mm)
Choose the spacing between rebars (typically 100-300mm or 4-12 inches)
Select direction: both directions for a grid, or single direction for one-way slabs
Enter edge distance (concrete cover) - typically 25-50mm (1-2 inches)
Specify overlap length if bars need to be spliced
Click Calculate to see the number of bars, total length, and weight

Rebar Calculation Formulas

1. Bars (Length) = (Width - 2×Cover) / Spacing + 1

2. Bars (Width) = (Length - 2×Cover) / Spacing + 1

3. Length per Bar = Dimension + 2×Overlap

4. Total Length = (Number of Bars) × (Length per Bar)

5. Weight = Total Length × Unit Weight (kg/m)

Rebar Size Specifications

#2 (6mm): 0.222 kg/m - Light reinforcement, wire mesh

#3 (8mm): 0.395 kg/m - Residential slabs, light structures

#4 (10mm): 0.617 kg/m - Standard residential slabs

#5 (12mm): 0.888 kg/m - Heavy residential, commercial slabs

#6 (16mm): 1.578 kg/m - Structural beams, columns

#7 (20mm): 2.466 kg/m - Heavy structural elements

#8 (25mm): 3.853 kg/m - Large beams, heavy columns

Tips for Rebar Installation

Standard spacing for residential slabs is 150-200mm (6-8 inches)
Concrete cover protects rebar from moisture - minimum 25mm for slabs
For exterior or ground contact, increase cover to 50-75mm
Overlap splices should be 40-60 times the bar diameter
Use rebar chairs or spacers to maintain proper cover distance
Tie bars together at intersections to prevent movement during concrete pour
Always follow local building codes for reinforcement requirements

About Reinforcement Steel (Rebar)

Rebar, short for reinforcing bar, is a steel bar or mesh used to strengthen and hold concrete in tension. Concrete is strong in compression but weak in tension, so rebar provides the tensile strength needed for structural integrity. Rebar comes in standard sizes designated by numbers (#2 through #18) corresponding to the bar diameter in eighths of an inch in imperial units, or by millimeter diameter in metric. It features surface deformations (ridges) that help bond with concrete. Common applications include concrete slabs, foundations, beams, columns, walls, and bridges.

Common Rebar Estimation Mistakes

Not accounting for concrete cover - reduces effective dimensions
Forgetting to add extra length for overlaps and splices
Using insufficient rebar spacing for the load requirements
Not considering both directions for two-way slabs
Underestimating edge conditions and corner reinforcement
Not ordering extra bars for waste and cutting adjustments (add 5-10%)

Rebar Calculator

Slab Dimensions

Rebar Settings