Rebar Calculator USA 2026
Calculate rebar bars, total linear feet and lap allowance for a reinforced slab grid at any bar spacing, plus the number of standard 20 ft sticks to buy.
Rebar Calculator USA 2026 — the quick answer
Calculate rebar bars, total linear feet and lap allowance for a reinforced slab grid at any bar spacing, plus the number of standard 20 ft sticks to buy.
| Formula | Bars per direction = (Span ÷ Spacing) + 1 → Total LF = bars × length, both ways, +10% laps |
|---|---|
| Category | Concrete |
| Cost basis | 2026 USA averages (USD) |
Output
Planning estimate
Time to use
Under a minute
Last reviewed
2026
Built for
DIYers & trades
Enter your measurements
Results
Bars lengthwise
15
each 20 ft
Bars widthwise
15
each 20 ft
Total rebar (with 10% laps)
660 linear ft
20 ft sticks to buy
33
Calculation steps
- 1.Bars lengthwise = (20 × 12 ÷ 18) + 1 = 15
- 2.Bars widthwise = (20 × 12 ÷ 18) + 1 = 15
- 3.Total = (15 × 20) + (15 × 20) = 600 LF
- 4.With 10% laps = 660 LF = 33 sticks of 20 ft
Includes a standard waste allowance. Verify with your supplier before ordering.
What this calculator does
Estimates the volume of ready-mix concrete you need — in cubic yards, cubic meters and 60/80 lb bag counts — plus a 10% waste allowance so you don't run short mid-pour.
When to use it
- Planning a slab, patio, footing, driveway or sidewalk pour.
- Comparing bagged vs. ready-mix truck pricing.
- Sizing rebar, mesh and vapor barrier by area.
Common mistakes
- Forgetting to convert thickness from inches to feet before multiplying.
- Ordering exact volume with zero waste — always add 5–10%.
- Ignoring compaction: over-excavated subgrade sinks the finished slab.
Pro tips
- Order 10% extra for slabs, 15% for uneven ground or complex forms.
- For driveways, use 6" thickness and #4 rebar at 18" on-center.
- Pour early morning in summer to avoid flash-set from heat.
What the Rebar Calculator works out for your rebar job
Calculate rebar bars, total linear feet and lap allowance for a reinforced slab grid at any bar spacing, plus the number of standard 20 ft sticks to buy.
Enter Slab length (ft), Slab width (ft), Grid spacing (in) and Bar stock length (ft) and the rebar calculator returns Bars lengthwise, Bars widthwise, Total rebar (with 10% laps) and 20 ft sticks to buy instantly — no signup, no spreadsheet and no install. Every figure updates as you type so you can test two or three rebar scenarios before you commit to an order or a bid.
Rebar numbers this page gives you
The output is written for a real supply run: quantities and figures you can hand to a supplier or drop straight into a bid for rebar work.
- Bars lengthwise — recalculated on every input change.
- Bars widthwise — recalculated on every input change.
- Total rebar (with 10% laps) — recalculated on every input change.
- 20 ft sticks to buy — recalculated on every input change.
How to estimate rebar step by step
The math behind this page is Bars per direction = (Span ÷ Spacing) + 1 → Total LF = bars × length, both ways, +10% laps. Nothing is hidden — the formula, the assumptions and the waste allowance are all printed on the page so you can re-check the result by hand.
Worked example: A 20 ft × 20 ft slab at 18 in OC: (20 × 12 ÷ 18) + 1 = 15 bars each way = 600 LF, +10% laps = 660 LF ≈ 33 sticks of 20 ft #4.
- Measure the rebar area or run and write down Slab length (ft), Slab width (ft), Grid spacing (in) and Bar stock length (ft).
- Enter the figures above and read the rebar result.
- Add the recommended waste allowance before you order.
- Save or download the estimate so your supplier and your crew work from the same numbers.
Rebar searches this page answers
Homeowners, DIYers and contractors reach this rebar page looking for the same handful of answers. Each of these is answered above with the formula shown:
- Rebar calculator
- How much rebar do I need
- Rebar estimator online
- Rebar quantity takeoff calculator
- Free rebar calculator app USA
- Rebar material calculator 2026
Before you order rebar: quick checklist
- Re-measure the rebar area once before ordering — a second check is cheaper than a second delivery.
- Keep the stated waste allowance in the order; cuts and breakage are normal on rebar work.
- Confirm coverage or unit size with your actual supplier — rebar pack sizes vary by brand.
More rebar planning tools
Pair this rebar estimate with the rest of BuildMate: a full calculator index, an AI planner that turns a plain-English description into a materials list, and step-by-step guides for the trade work itself.
Targeted searches: rebar calculator · how much rebar do I need · rebar estimator online · rebar quantity takeoff calculator · free rebar calculator app USA · rebar material calculator 2026
Safety notice: Reinforcement design for structural footings, walls and suspended slabs should be confirmed against local code or an engineer's drawings.
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Disclaimer: This is a planning estimate produced from the formula shown above. Actual quantities vary with site conditions, layout, offcuts and installer practice. Verify with your supplier or contractor before ordering, and see our methodology.
How it works
- 1Enter slab length and width in feet.
- 2Enter grid spacing — 18 in on center is typical for residential slabs, 12 in for heavier loads.
- 3We count bars in both directions, total linear feet, add 10% for laps and ties, and convert to 20 ft sticks.
Formula
Worked example
A 20 ft × 20 ft slab at 18 in OC: (20 × 12 ÷ 18) + 1 = 15 bars each way = 600 LF, +10% laps = 660 LF ≈ 33 sticks of 20 ft #4.
Frequently asked questions
What size rebar for a residential slab?
#4 (1/2 in) bar at 18 in on center is the common residential standard; #5 for driveways with heavy vehicles.
How long should laps be?
A typical lap for #4 bar is 25 in — roughly 40 bar diameters. The 10% allowance covers it.
Can I use wire mesh instead?
6×6 W1.4 mesh is acceptable for light slabs, but rebar gives better crack control in driveways and footings.
How do I use the Rebar Calculator?
Enter Slab length (ft), Slab width (ft), Grid spacing (in) and Bar stock length (ft). The rebar calculator instantly returns Bars lengthwise, Bars widthwise, Total rebar (with 10% laps) and 20 ft sticks to buy, along with the formula and every calculation step so you can verify the result.
How much rebar do I need?
It depends on your measurements, so run the rebar numbers above rather than using a rule of thumb. The calculator applies the standard trade formula plus a stated waste allowance, which is what stops you from coming up short mid-job.
What does the Rebar Calculator include in its result?
It reports Bars lengthwise, Bars widthwise, Total rebar (with 10% laps) and 20 ft sticks to buy. The underlying formula is Bars per direction = (Span ÷ Spacing) + 1 → Total LF = bars × length, both ways, +10% laps.
Is the Rebar Calculator free, and does it work on mobile?
Yes — it's free, needs no account, and runs in the browser on phone, tablet and desktop. Nothing is installed and your saved rebar estimates stay on your own device.
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