Rebar Calculator

How It Works

Math is hard enough; take a load off and use our free concrete rebar calculator to quickly calculate how much rebar you'll need for your next project.

Tip:Your calculations will be saved automatically, so no need to worry about your progress being erased.

Let's get calculating!

Step-by-Step Tutorial

Calculating how much rebar you need has never been easier. Follow these 2 simple steps to make the process seamless and efficient. Let's get started!

Step 1: Choose Your Unit Type

Select your unit type. This will likely be defaulted to your countries unit of measurement. Your unit type will be automatically saved for when you come back the next time.

Step 2: Add Your Rebar Measurements

Input the dimensions that you've measured for your slab or footing. This will include the length and width of the area, the edge clearance, spacing between the rebar and the length of the rebar.

After that, your results will be shown!

Pretty easy, isn't it?

Edit, Save and Repeat

Now you can easily measure all of your rebar projects. Bookmark this page and your calculations will be here when you return. When you're done, reset the calculator and start with a fresh one.

How to Calculate Rebar for a Concrete Footing

When planning a concrete footing, calculating the right amount of rebar is essential for strength, durability, and safety. The math behind rebar calculation involves determining the number of bars needed based on the slab’s dimensions and the spacing between each rebar line.

To start, measure the length and width of your slab in feet or meters. Then decide on the spacing between rebar lines, which is typically 12 inches (or 1 foot) apart for residential and light commercial slabs.

Here’s the basic formula:

• Number of bars in one direction = (Slab dimension / Spacing) + 1
• Multiply by 2 to account for both lengthwise and widthwise rebar.
• Total rebar length = Number of bars × Length of each bar
• Convert this into feet or meters and divide by the standard rebar length (e.g., 20 feet) to get the number of rebar pieces needed.

For example, a 20x20 footing with 12-inch spacing would need:

• (20 ÷ 1) + 1 = 21 bars in each direction
• Total = 42 bars
• Total length = 21 × 20 (for each direction) = 420 feet of rebar
• Total pieces = 420 ÷ 20 = 21 pieces (rounded up as needed)

Don’t forget to account for overlaps (called “lap splices”) and waste, usually adding 10–15% to your final number.