Free reinforcement estimator

Rebar Calculator

Estimate rebar count, spacing, total length, total weight, waste, and cost for slabs, footings, piers, columns, and walls. Use it to plan materials before you order steel or ask a supplier for a quote.

Spacing and layout Weight and waste Slab and footing modes Copy and CSV export
Rebar calculator preview with spacing, total length, weight, and cost
Instant estimate 24 bars 316 lb

Estimate slab reinforcement before you order steel

Choose a project type, enter the slab or footing dimensions, and the calculator estimates bar spacing, bar count, total length, total weight, and material cost. Results are planning estimates only and do not replace structural design or local code requirements.

ProjectSlab grid
Bar size#4
Spacing12 in

Project dimensions

Use slab mode for flat pours, footing mode for continuous runs, pier mode for columns, and wall mode for a vertical pour.

Rebar inputs and cost

Defaults are editable. Use the same price assumptions you would give a supplier or estimator.

What the calculator estimates

The calculator converts the project dimensions into a rebar layout, then estimates the number of bars, total length, total weight, and a planning cost.

Good default spacing

Many DIY slabs start with 12 in on center. Heavier loads, wider spans, and structural details can require tighter spacing or a different reinforcing pattern.

Planning note

Rebar size, spacing, lap lengths, and placement rules vary by project and local code. Use this as a material estimate, not structural design advice.

Formula used

  1. Convert all dimensions to feet.
  2. Estimate the number of runs in each direction from the spacing.
  3. Count main bars and secondary bars for the selected layout.
  4. Add lap and waste allowances.
  5. Multiply total length by the selected bar weight to get total weight and cost.
How much rebar do I need for a slab?

It depends on slab size, spacing, bar size, and whether you are using one mat or two. This page estimates material only, so a structural plan should still come from your builder or engineer.

What is the best rebar spacing for a slab?

There is no one universal spacing. A common planning starting point is 12 inches on center, but the correct spacing depends on load, slab thickness, soil, and local code.

Does this replace an engineer or code check?

No. It is a material planning tool. It does not size reinforcement for structural safety, soil conditions, frost depth, or permit requirements.

Can I copy the estimate into a bid request?

Yes. The copy and CSV buttons help you share a concise estimate with a supplier, contractor, or project partner.