Rebar Material Calculator
Find how many bars a slab's rebar grid takes each way, their total length and weight, and how many stock bars to buy.
Change the values and press Calculate to work out your own figures.
Enter the slab's length and width, the bar spacing and the edge clearance.
Show the working
- grid = slab − 2 × clearance
- bars each way = ⌈grid side ÷ spacing⌉ + 1
How to use it
Enter the slab's length and width, the bar spacing and the edge clearance.
Lengths can be decimals, fractions or tape entries such as 12' 6 1/2" (in feet or inches). Prices are optional.
Key facts
grid = slab − 2 × clearance bars each way = ⌈grid width ÷ spacing⌉ + 1, each as long as the other grid side
Typical sizes
#3 bar suits patios and driveways, #4 walls and columns, #5 footings. Slab grids are commonly 12–24 in on center, 2–3 in from the edges; follow your plans or local code.
Questions
How many bars for a 10 × 10 ft slab at 18 in?
16: 8 each way, each 9 ft 6 in with 3 in clearance.
Formulas
grid = slab − 2 × clearance bars each way = ⌈grid width ÷ spacing⌉ + 1, each as long as the other grid side
Sources
Limitations
- Material densities are typical values (the midpoint of the commonly published range); real loads vary with moisture, grading and compaction, so check with your supplier or type in their density.
- Tank results are the geometric volume; real tanks have wall thickness and fittings.