Rebar Grid Calculator

Plan rectangular rebar grids, stock-bar cuts, purchasing quantities, optional weight and cost.

Enter the layout required by your plans or project specification. These defaults are examples, not reinforcement recommendations.

Plan your grid and stock bars

Your slab

Slab length (ft)

Use decimal feet: 12.5 means 12 ft 6 in.

Slab width (ft)

Rebar layout

Maximum rebar spacing (in on center)

Use the spacing from your project specification; custom values are accepted.

Edge centerline clearance (in)

Distance from slab edge to outside bar centerline. This is not concrete cover.

Stock and splices

Stock bar length (ft)

Enter the length you plan to buy, such as 10, 20 or 40 ft.

Lap/splice allowance (in)

Enter the lap length required by your project specification if bars must be spliced. RockUtility does not determine required lap length; 0 adds no overlap.

Purchasing allowance

Applied once to the cutting layout’s stock-bar count, then rounded up.

Optional weight and cost

Rebar size for weight estimate

Size is not a structural recommendation.

Price per stock bar ($, optional)

Use your supplier’s price. Leave blank to omit cost.

Your rebar grid

Bars running lengthwise: runs
Bars running widthwise: runs
Total rebar in grid: linear ft
Stock bars to buy: bars

Layout and purchasing details

Actual spacing across width: in
Actual spacing along length: in
Each lengthwise run: ft
Each widthwise run: ft
Lengthwise total: ft
Widthwise total: ft
Stock bars before allowance
Additional allowance bars
Purchasing allowance: %
Purchased stock length: ft
Physical cut pieces
Splices modeled
Cut-piece length including lap: ft
Unused offcuts before allowance: ft

Shopping list

Top-down grid

Estimated cutting layout

Deterministic cutting layout with remnant reuse; not a guarantee of the fewest possible stock bars. No cutting kerf is included. Additional allowance bars remain spare stock.

Cutting patterns before purchasing allowance
Stock bars	Pieces per bar (ft)	Offcut per bar (ft)

How it works

How the grid is calculated

Your spacing is treated as the maximum gap between bar centerlines. We round the number of spaces up so actual spacing does not exceed that value, with outside bars at your entered edge clearance.

Which direction is which?

Lengthwise bars run along the slab’s length, but their count is determined across its width. Widthwise bars run across the width, but their count is determined along the length.

Each run ends at the entered clearance. Long runs are split into stock-length segments and a final cut piece, including your entered lap at each splice. Short pieces reuse remaining stock where the deterministic layout allows. Purchasing allowance is then added once to stock-bar count.

Assumptions and useful information

Rectangular grid only, with straight runs and no hooks, bends, development length or embedment added. Edge centerline clearance is not concrete cover. Clearance leaving zero usable length or width is rejected.

Lap positions, splice staggering and minimum piece lengths are not designed. Zero lap adds no overlap; it does not approve splicing. Nominal weight is based on purchased stock length. Cost uses only your entered stock-bar price.

For large grids, the diagram shows representative lines and labels the actual counts. Layouts exceeding 5,000 cut pieces are rejected to keep this worksheet responsive.