Rebar Calculator
Lay out the rebar grid for a concrete slab: bars in each direction, total linear feet, and how many sticks to buy at your supplier's stock length.
Results
Total linear feet
635ft
Sticks to buy
37sticks
Bars one way
16bars
Bars other way
21bars
Linear feet is the raw grid. The stick count is figured per bar, so a 15 ft bar cut from a 20 ft stick counts as a whole stick and the offcut is already in the number. Add about 10% to the footage for lap splices where bars overlap.
Figures last checked . Sources are listed below.
How the rebar calculator works
Slab rebar is a grid, with bars running both directions at a fixed spacing. How many run lengthwise depends on how many fit across the width, and the other direction works the same way in reverse. One extra bar goes into each direction so both edges are covered.
Formula: bars one way = (width ÷ spacing) + 1. Bars the other way = (length ÷ spacing) + 1. Total linear feet = (bars one way × length) + (bars other way × width).
Once you know your rebar grid, head to the Concrete Calculator with the same slab dimensions to work out the cubic yards or bags you'll need to pour over it.
Reinforcing a block wall rather than a slab? The Concrete Block Calculator works out the blocks, mortar and grout for the cores you fill.
Sources
Frequently asked questions
12 inches on center for residential slabs like driveways and patios. Sidewalks and small pads sometimes go out to 18-24 inches. Those are conventions, not rules: local code or an engineer's spec beats both, and on anything structural that is the number to build to.
Bars in one direction get spaced across the slab's other dimension, plus one extra so both edges are bracketed. That plus-one is the step people forget, and it is why a hand count usually comes out one bar short per direction. The calculator does both directions and totals the linear footage.
20 ft and 40 ft sticks are the standard stock lengths, sold full or cut in half. Set the stick length field to whatever your supplier carries, since that determines how many you buy and how much you end up cutting off.
Yes. Bars that meet have to overlap in a lap splice, not butt end to end. The lap length is set by the plans or local code and grows with bar size. For bars in concrete block walls, CMHA TEK 12-06A gives a minimum of 12 inches or 40 bar diameters, whichever is greater: 20 inches for #4 bar and 25 inches for #5. Add roughly 10% to the linear footage above to cover laps and offcuts, or more if your laps are long.
Yes. Bar size changes weight and strength, not geometry, so a #3 grid and a #5 grid at the same spacing need the same number of bars and the same linear footage. Only the tonnage and the price change.
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