Concrete Rebar Calculator: 20x20 = 31 Sticks

A concrete rebar calculator is a material takeoff tool. It helps estimate how many bars, how many linear feet, how many 20 ft sticks, and how much rebar weight or material cost may be needed before a concrete slab, garage floor, footing, driveway pad, or shed base is quoted.

Answer first: a 20x20 slab rebar grid at 18 in spacing with 3 in edge clearance needs about 546 linear ft before waste. With 10% waste, that is about 601 linear ft, or 31 common 20-ft sticks before the final cut list, lap splice plan, dowels, chairs, tie wire, delivery, labor, and inspection scope are confirmed.

Use the Rebar Spacing Calculator to turn an approved maximum spacing into grid bars, actual spacing, linear feet, stock sticks, approximate weight, chair count, and material cost. Use this guide to turn slab dimensions, bar spacing, edge clearance, stock length, and waste into a practical rebar quantity. Use the Concrete Slab Calculator reinforcement takeoff for a live slab grid, stick-count, and quote-scope worksheet. Use the Concrete Slab Calculator for concrete volume, the Concrete Footing Calculator for footing yardage, and the Concrete Garage Slab Calculator for garage slab cubic yards and bag counts. If you need to compare concrete and steel as one budget line, use the Reinforced Concrete Cost per Cubic Yard Guide. For a small pad-specific reinforcement check, use the Concrete Pad Rebar Spacing Guide to compare grid spacing, chairs, laps, edge clearance, mesh, and fiber scope.

This page does not design reinforcement. Rebar size, spacing, cover, laps, dowels, chairs, and inspection requirements should follow the project drawing, local code, or a qualified professional.

Rebar calculator query map

The differentiated workflow is grid takeoff -> buy list -> quote audit. Many calculators stop at bar count. This guide keeps going into stock lengths, weight, chairs, laps, inspection timing, and the contractor bid lines that often hide inside "reinforced concrete."

Quick answer

For a rectangular slab grid, count the bars in each direction, multiply by the bar length in that direction, then add overlap and waste. A 20 ft by 20 ft slab with rebar at 18 in spacing and 3 in edge clearance needs about 28 grid bars before laps: 14 bars running one way and 14 running the other. Each bar is about 19.5 ft long, so the grid is about 546 linear feet before waste.

With 10% waste, that example is about 601 linear feet. If you buy common 20 ft sticks, that is roughly 31 sticks before adjusting for the actual cut plan, lap details, local stock lengths, and any extra dowels or edge bars.

20x20 rebar answer in one screen

Use this as a quick planning screen before opening the live calculator.

Before ordering, ask whether the quote also includes lap splices, bent bars, dowels, chairs, tie wire, cutting, delivery, labor, and inspection coordination.

What a rebar calculator should estimate

A useful rebar calculator should keep the steel takeoff separate from the concrete quantity. The slab calculator tells you cubic yards. The rebar calculator tells you how much steel may be in the slab.

Competitor tools often lead with length, width, spacing, edge clearance, bar length, and price. For this site, the concrete-specific step is to connect the steel takeoff back to the slab, footing, garage, shed, or driveway quote.

Recent calculator pages in this space tend to win because they are fast and visual: enter slab size, pick spacing, see bar count. The gap is that many of them stop before the buying decision. For a real quote, the material count is only useful after it is tied to stock length, bar weight, cut waste, support method, and inspection responsibility.

Slab rebar grid formula

For a rectangular slab with a simple two-way grid:

usable width in = slab width in - 2 x edge clearance in
usable length in = slab length in - 2 x edge clearance in

Bars running along the slab length are spaced across the slab width:

bars along length = floor(usable width in / spacing in) + 1
length of each bar = slab length ft - 2 x edge clearance ft

Bars running along the slab width are spaced across the slab length:

bars along width = floor(usable length in / spacing in) + 1
length of each bar = slab width ft - 2 x edge clearance ft

Then add both directions:

total linear feet =
  bars along length x length of each bar
  + bars along width x length of each bar

Finally add lap and waste:

order linear feet = total linear feet x (1 + waste percentage)

This formula is a takeoff shortcut, not a reinforcement design. It assumes a rectangular layout and does not decide whether the slab needs rebar, wire mesh, fiber, thickened edges, dowels, or engineered reinforcement.

Example: 20x20 slab rebar at 18 in spacing

Assume:

• Slab size: 20 ft x 20 ft
• Spacing: 18 in each way
• Edge clearance: 3 in
• Waste factor: 10%
• Stock length: 20 ft sticks

Usable layout:

20 ft = 240 in
usable distance = 240 - 6 = 234 in
234 / 18 = 13
13 + 1 = 14 bars each direction

Each bar stops 3 in from each edge:

bar length = 20 ft - 0.5 ft = 19.5 ft

Total grid length:

14 x 19.5 + 14 x 19.5 = 546 linear feet
546 x 1.10 = 600.6 linear feet after waste

At 20 ft per stick:

600.6 / 20 = 30.03
round up to 31 sticks

That is a planning takeoff. The real order can change if the plan requires lap splices, additional perimeter bars, dowels, beam steel, bent bars, or a different stock length.

Quick rebar grid examples

These examples use a simple two-way slab grid, 3 in edge clearance, and 10% waste. They do not include laps, extra perimeter bars, dowels, thickened edges, chairs, ties, or cut-list losses.

The "20 ft sticks by length" column is a minimum material-length check. A field cut list can require more sticks when bars are longer than half a stick and offcuts cannot be reused.

Rebar size and weight table

Rebar size changes weight, handling, delivery, and price. Use the project plan or local guidance for the required size.

Weight estimate:

rebar weight = total linear feet x lb per ft

For the 20x20 example above, 600.6 linear feet of #4 rebar is:

600.6 x 0.668 = about 401 lb

That is only the steel weight. It does not include chairs, tie wire, cutting, bending, delivery, labor, inspection, or engineering.

Rebar cost formula

Rebar cost can be estimated from stick count or from weight, depending on how the supplier prices material.

For stick pricing:

rebar material cost = number of sticks x price per stick

For weight pricing:

rebar material cost = total rebar weight x price per lb

For a fuller quote check:

reinforcement scope =
  rebar material
  + chairs, tie wire, dowels, anchors, and supports
  + cutting, bending, delivery, and labor
  + inspection coordination if required

Keep this separate from concrete cost. Use the Concrete Cost Calculator for ready-mix or bagged concrete pricing, then add reinforcement as a separate line item.

Rebar, mesh, and fiber are different scopes

Rebar, wire mesh, and fiber are not interchangeable line items in a quote. They may all appear under "reinforcement," but they change cost, placement, and expectations differently. If you are comparing a bid that uses rebar against a bid that uses mesh, use the Rebar vs Wire Mesh Cost Guide to normalize the material, support, overlap, labor, and inspection scope.

Do not accept a quote that only says "reinforced concrete" if the project requires a specific bar size, spacing, mesh type, or dowel detail.

Garage slab rebar checks

A garage slab estimate often starts with cubic yards, but reinforcement can change the bid and inspection conversation. Use the Concrete Garage Slab Calculator for volume, then use this page to ask whether the garage slab has a rebar grid, wire mesh, fiber, thickened edge steel, dowels, or no reinforcement.

For a written garage scope, ask:

• What bar size or mesh is included?
• What spacing is used each way?
• Are chairs or supports included?
• Are thickened edges or aprons reinforced separately?
• Does the work require inspection before the pour?

If a garage bid is much cheaper, reinforcement is one of the first missing scope lines to check.

Footing rebar and dowel checks

Footing rebar is usually driven by the approved plan, not by a generic calculator. Use the Concrete Footing Calculator for the concrete volume, then keep the reinforcement details separate.

For footing work, confirm:

• Bar size and number of continuous bars.
• Horizontal and vertical placement.
• Lap length and splice locations.
• Chairs, supports, dowels, anchor bolts, or hold-down hardware.
• Inspection timing before concrete delivery.

A footing concrete estimate can ignore rebar displacement for ordinary material planning, but it should never ignore rebar timing. A truck that arrives before steel, forms, and inspection are ready can create delay charges or a missed pour window.

Shed base, patio, and driveway checks

Small slabs may use no rebar, wire mesh, fiber, or a simple grid depending on load, soil, base preparation, and local practice. Do not choose reinforcement only from square footage.

Use these project guides to keep the context clear:

For slab thickness context, see the Concrete Slab Thickness Guide. For base stone below the slab, use the Gravel Base Calculator for Concrete.

Quote checklist

Use this checklist when a bid includes concrete reinforcement.

Red flags

Sources and checks

Use public calculators and supplier references as sanity checks, not as design authority.

The safe workflow is to use the calculator for takeoff, use the plan or local professional for reinforcement requirements, and use the quote checklist to make sure steel is not hidden inside a vague lump sum.

FAQ

How do I calculate rebar for a concrete slab?

Count the bars running each direction, multiply by the bar length in that direction, then add lap and waste. For a rectangular grid, spacing and edge clearance control the bar count.

How many sticks of rebar do I need?

Divide the estimated linear feet after waste by the stock length, then round up. Treat that as a minimum length check. A real cut list can require more sticks if offcuts cannot be reused.

Does rebar reduce the concrete yardage?

For most homeowner-level material planning, no. Rebar displacement is usually small compared with uneven forms, trench variation, waste, and supplier rounding. Keep concrete volume and rebar takeoff separate.

What rebar spacing should I use for a slab?

Use the project drawing, local code, or a qualified professional. A calculator can estimate material from a spacing value, but it should not choose the spacing for structural work.

Is wire mesh the same as rebar?

No. Wire mesh and rebar are different reinforcement scopes. A quote should say which one is included, where it is placed, how it is supported, and whether overlaps or chairs are included.

Should garage slabs use rebar?

It depends on loads, soil, base preparation, slab thickness, local practice, and code. Use the garage slab calculator for concrete volume, then confirm the reinforcement design separately.

Next step

Use the Concrete Slab Calculator or Concrete Footing Calculator for the concrete quantity first. Then use this rebar guide to check steel length, stick count, weight, cost, chairs, ties, and inspection details before comparing contractor quotes.