Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Total rebar needed
341.0
linear ft
20ft stock lengths to buy
18
Bars running lengthwise
15
Bars running widthwise
8
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter slab length (ft).
- 2Enter slab width (ft).
- 3Enter grid spacing (in).
- 4Enter edge clearance (in).
- 5Enter lap splice allowance (%).
- 6Read your total rebar needed on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
Reinforcing a concrete slab or footing with rebar means laying a grid of bars running in both directions at a set spacing, commonly 12, 16, or 18 inches on-center depending on the load and local code requirements, and the total linear footage needed is the sum of every bar run in both the length and width directions. This calculator takes your slab's length and width, your on-center spacing, and edge clearance (rebar is typically kept 2-3 inches back from the slab edge), calculates how many bars run in each direction, multiplies by the run length, sums both directions, and adds a lap splice allowance since rebar comes in fixed stock lengths (commonly 20 feet) and adjacent bars need to overlap by roughly 12-24 inches (or per code, often 40× the bar diameter) at any splice point. It also converts total linear feet into the number of standard 20-foot stock lengths needed to buy, since that's how rebar is typically sold at a supply yard.
Worked example
Using the values the calculator loads with:
Inputs
- Slab length: 20 ft
- Slab width: 10 ft
- Grid spacing: 16 in
- Edge clearance: 3 in
- Lap splice allowance: 10 %
Results
- Total rebar needed: 341
- 20ft stock lengths to buy: 18
- Bars running lengthwise: 15
- Bars running widthwise: 8
What each field means
Inputs
- Slab length (ft)
- The slab length used in the calculation, measured in ft. Starts at 20 ft so you have a working example on load.
- Slab width (ft)
- The slab width used in the calculation, measured in ft. Starts at 10 ft so you have a working example on load.
- Grid spacing (in)
- The grid spacing used in the calculation, measured in in. Starts at 16 in so you have a working example on load. Accepted range: 6–36 in.
- Edge clearance (in)
- The edge clearance used in the calculation, measured in in. Starts at 3 in so you have a working example on load. Accepted range: 1–6 in.
- Lap splice allowance (%)
- The lap splice allowance used in the calculation, measured in %. Starts at 10 % so you have a working example on load. Accepted range: 0–25 %.
Results
- Total rebar needed
- linear ft
- 20ft stock lengths to buy
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Bars running lengthwise
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Bars running widthwise
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
What rebar spacing is standard for a slab?
12-18 inches on-center is common for residential slabs, with tighter spacing (12 in) used for driveways or slabs bearing vehicle loads and wider spacing (16-18 in) for patios and sheds.
What size rebar should I use?
#3 (3/8 in) or #4 (1/2 in) rebar covers most residential slab and footing applications; heavier structural work or engineered designs may call for #5 or larger — check your local code or engineer's spec.
How much overlap does rebar need at a splice?
A common rule of thumb is 40 times the bar's diameter, though many residential jobs use a simpler 12-24 inch overlap; always defer to your local code or engineer's specification where one applies.
Do I need rebar or is wire mesh enough?
Wire mesh controls surface cracking in light-duty slabs like patios, while rebar provides real structural reinforcement for load-bearing slabs, footings, and anything supporting a structure or vehicle weight — check your code for which is required.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Wire Mesh Sheets Calculator
Sheet count of welded wire mesh needed to reinforce a slab, with overlap.
20x20 Concrete Slab Calculator
Yardage for a full 400 sq ft slab — garage, large patio, or detached garage footing pad.
Concrete Cubic Yards Calculator
Convert a slab, footing, or pad's dimensions straight into cubic yards of ready-mix.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Rebar Linear Feet Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/rebar-linear-feet-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/rebar-linear-feet-calculator" target="_blank" rel="noopener">Rebar Linear Feet Calculator — RevenueLab</a> (2026).</p>
Source: [Rebar Linear Feet Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/rebar-linear-feet-calculator) (2026).