Rebar Calculator — Bars, Linear Feet & Weight

Quick answer: a 10 × 10 ft slab with #4 rebar at 12 in on center needs about 11 bars each way — 220 linear feet, roughly 147 lb of steel.

Rebar is counted as a grid: bars running each direction, set in from the edges by the cover, spaced on center. This calculator gives you the bar count each way, total linear feet (with optional lap splices), the steel weight for the bar size you picked, and how many 20-ft sticks to buy.

It's built for slabs, patios and driveways — the residential cases where a grid of #3–#5 bar is typical. Structural designs (footings, walls, engineered slabs) should follow your plan's schedule.

How to use it

Measure the slab length and width in feet.
Enter your bar spacing — 12 in on center is common for residential slabs; 16–18 in for lightly loaded patios. Check your plan if you have one.
Set the edge cover (2 in is typical for slabs poured on grade) and pick the bar size.
Read the result: bars each way, total linear feet (with laps), weight, and 20-ft sticks to buy — plus a cost estimate at your stick price.

How it works

Bars per direction = ceil((dimension − 2 × cover) ÷ spacing) + 1. Total length = Σ (bars × run length) + lap allowance (40 × bar diameter per splice). Weight = total length × nominal weight (ASTM A615: #4 = 0.668 lb/ft).

Nominal unit weights per ASTM A615: #3 = 0.376, #4 = 0.668, #5 = 1.043, #6 = 1.502, #7 = 2.044, #8 = 2.670 lb/ft.
Lap splices assumed at 40 × bar diameter (a common rule of thumb — codes vary by bar size, concrete strength and location).
Sticks assumed 20 ft (standard mill length); count rounded up.
This is a quantity estimator — reinforcement design belongs to a structural plan or engineer.

Worked example

A 10 × 10 ft slab, #4 bar at 12 in on center with 2 in cover: (120 − 4) ÷ 12 = 9.67 → 10 spaces → 11 bars each way. Total length = 11 × 10 ft × 2 directions = 220 linear ft ≈ 147 lb (220 × 0.668). At 20 ft per stick that's 11 sticks — 10 ft runs need no splices.

Quick reference

Rebar sizes — nominal weight

Bar	Diameter	Weight (lb/ft)	Weight per 20-ft stick
#3	3/8 in	0.376	7.5 lb
#4	1/2 in	0.668	13.4 lb
#5	5/8 in	1.043	20.9 lb
#6	3/4 in	1.502	30.0 lb
#7	7/8 in	2.044	40.9 lb
#8	1 in	2.670	53.4 lb

Typical slab spacing

Application	Typical spacing	Typical bar
Patio / walkway slab	16–18 in OC	#3 or #4
Driveway slab	12–16 in OC	#4
Structural slab / engineered	per plan	per plan
Footings	per plan (continuous bar)	per plan

FAQ

What spacing should rebar be in a slab?

Residential patios and driveways typically use #4 bar at 12–18 in on center each way, set 2 in in from the edges. Your plan or local code governs — 12 in OC is the common default for driveways, 16–18 in for lighter slabs.

How many sticks of rebar do I need?

Divide total linear feet by 20 (standard stick length) and round up. A 10 × 10 slab with #4 at 12 in OC is 220 ft — 11 sticks before laps, about 13 with lap splices.

How long should rebar lap splices be?

A common rule of thumb is 40 × bar diameter (so 20 in for #4 bar), but code requirements vary with bar size, concrete strength and whether the bar is in tension or compression. Check your plan for the required splice.

Do I need rebar or is wire mesh enough?

For a patio or walkway on stable ground, welded wire mesh (6×6–W2.9×W2.9) is often used for crack control. Rebar adds structural reinforcement — typical for driveways and anything vehicle-loaded. When in doubt, follow the plan.

How much does rebar cost?

Around $8–15 per 20-ft stick depending on size and region ($0.75–1.10/lb). A typical driveway slab (16 × 24 ft, #4 at 16 in OC) runs roughly $90–150 in bar.

Related calculators

Concrete Calculator

Sources & verification

Data verified: October 11, 2026.

Nominal weights: ASTM A615 (standard specification for deformed carbon-steel bars).
Spacing & laps: common residential practice; IRC/ACI govern structurally.

Estimates are for planning only — always confirm quantities with your supplier and check local building codes before you buy or build.