A rebar calculator estimates how many pieces and how many linear feet of reinforcing bar you need for a concrete slab, patio, driveway or footing. Enter the dimensions of the area, the spacing between bars and the length of each bar, and it calculates the total.
For a grid, calculate each direction separately. The number of bars = (width ÷ spacing) + 1. For a 20 × 12-foot slab with bars every 12 inches (1 foot), you’d need (12 ÷ 1) + 1 = 13 bars running 20 feet long, and (20 ÷ 1) + 1 = 21 bars running 12 feet long. That’s 13 × 20 + 21 × 12 = 512 linear feet. Subtract a few inches for edge cover on each end, and add extra for overlaps where bars are spliced, often 30 to 40 times the bar diameter.
Rebar sizes in the US are numbered by eighths of an inch: #3 is 3/8 inch, #4 is 1/2 inch and #5 is 5/8 inch. Driveways and patios often use #3 or #4 bars, while footings and structural elements may require larger sizes, based on engineering and code requirements.
Tips: keep rebar elevated in the middle of the slab using chairs or supports, maintain proper concrete cover from the edges and buy a little extra for cuts. Structural projects should follow local building codes or a licensed engineer’s design.
Tips for getting accurate results from the Rebar Calculator: double-check that every input uses the right units, enter numbers without commas or symbols, and run the calculation a second time with a quick estimate in your head to confirm the answer looks reasonable.
How to use the Rebar Calculator on Minedit: enter your values in the fields, press calculate, and review the step-by-step breakdown under the result. If something looks off, change one input at a time to see how it affects the answer, which is also a great way to learn the math behind it.
Learn more on Wikipedia’s rebar article. Find yardage, square footage and board feet calculators on Minedit.