Enter your slab dimensions and bar spacing to get total bar count, linear feet, and 20-ft stick count.
The Rebar Calculator helps you figure out exactly how much material to buy before you order a truck or make a hardware store run. Enter your slab dimensions and bar spacing to get total bar count, linear feet, and 20-ft stick count. Instead of guessing at cubic yards or bag counts and hoping it's close, you enter the numbers you already have — the measurements from your plan, tape measure, or job site — and get a precise, ready-to-order figure back in seconds.
This tool is built for two kinds of people: contractors running a fast takeoff between jobs who need a number they can call into a supplier immediately, and homeowners or first-time DIYers who don't want to either overspend on wasted material or come up short mid-pour. Every calculator on ConcreteYard uses the same standard, industry-typical assumptions — 150 lb per cubic foot for normal-weight concrete, standard bag yields, and common mix ratios — so the numbers here should line up closely with what your supplier or hardware store confirms when you place the order.
Whether you're pricing out a job, planning a delivery, or just want to know how much to buy at the store today, this calculator gives you a number you can act on immediately — no spreadsheet, no account, and no guesswork required.
o.c. = on-center spacing, measured from the middle of one bar to the next. #3\u2013#4 rebar at 12\u201318in o.c. is common for residential slabs.
1. Measure accurately. Get exact dimensions in the units the calculator asks for — feet for length and width, inches for thickness are the most common setup. A rough guess in, a rough number out; precise measurements are what make this tool worth using over a mental estimate.
2. Enter your numbers. Fill in the fields above with your project's actual measurements. Default values are pre-filled as a sane starting point — replace every one of them with your real numbers before you rely on the result.
3. Adjust the settings. Where available, set your waste percentage, bag size, or price per yard to match your job. These small adjustments are what separate a rough ballpark from an order-ready figure.
4. Read the batch ticket. Click calculate and use the highlighted total as your order quantity — it already accounts for waste and rounds to a practical ordering increment where relevant.
| Application | Typical Spacing |
|---|---|
| Residential slab | 12\u201318 in o.c. |
| Driveway | 12 in o.c. |
| Footing (single/double bar) | N/A \u2014 continuous bar |
| Structural slab | Per engineer spec |
Light-duty slabs (patios, sidewalks) often use welded wire mesh instead of rebar. Driveways, garage floors, and anything structural typically call for rebar on a grid \u2014 this calculator sizes that grid from your slab dimensions.
Divide each dimension by your bar spacing to get bar count in each direction, then multiply by the perpendicular length and sum. This calculator does that math and converts to 20-ft stick count.
#3 (3/8in) or #4 (1/2in) rebar is standard for residential slabs, typically spaced 12-18in on-center in a grid pattern.
Skipping the waste factor. Uneven subgrade, formwork gaps, and simple spillage routinely eat 5–10% of your raw calculated volume. Ordering the exact math-perfect number is one of the most common ways to come up short mid-pour.
Rounding down instead of up. Ready-mix trucks deliver in fractions of a yard, but suppliers set order minimums. If your number lands at 4.1 yards, round to 4.25 or 4.5, not down to 4.
Mixing up units. Thickness is almost always in inches while length and width are in feet — plugging inches into a feet field (or vice versa) is the single most common calculator input error.
Treating irregular shapes as one rectangle. An L-shaped or curved area isn't one simple calculation. Break it into rectangles, run each section separately, and add the totals together for an accurate figure.
Order slightly more than the bare minimum — a short-load fee for a second truck almost always costs more than the extra material would have. Confirm your supplier's order minimum and short-load fee before you finalize a quantity that's close to the cutoff.
Check the weather. Concrete needs temperatures generally above 40°F to cure properly without special cold-weather additives, and pouring in direct heat or high wind can cause the surface to dry and crack before it has a chance to properly set.
Have everything staged before the truck arrives — forms set, base compacted, tools (screed board, bull float, edger) on site, and enough hands to place and finish the pour before it starts to set.
Plan your control joints in advance for any flatwork. Joints control where concrete cracks as it cures and shrinks — skipping them doesn't prevent cracking, it just makes the cracks unpredictable.
Yes — it uses standard, industry-typical formulas and material assumptions (150 lb/cu ft concrete, standard bag yields, common mix ratios). For structural or permitted work, always confirm final quantities with your supplier or engineer.
No. Every calculator on ConcreteYard runs entirely in your browser, works instantly, and requires no sign-up, login, or download.
Yes — every tool on this site is built to work the same on a phone as it does on a desktop, so you can run the numbers standing at the job site before you call in an order.
Every tool below shares the same 150 lb/cu ft mix assumption, so figures stay consistent across your takeoff.