Rebar Cutting Optimization: Reducing Waste From Stock Lengths

Rebar cutting optimization means planning which pieces are cut from which stock bars so you use as few bars as possible and leave as little offcut as possible. Instead of cutting each bar mark from its own stock lengths, pieces of the same size from across the job are combined so the short pieces fill the gaps left by the long ones. On a job with many marks, that alone can save several stock bars per size and turn scattered offcuts into one or two usable remnants.

This post explains where cutting waste comes from, the methods used to reduce it (by hand, in Excel and in software), and a worked example. If you need to build the cutting list first, start with how to make a rebar cutting list.

Where rebar cutting waste comes from

Every cut length comes out of a stock bar. Canadian rebar is supplied in standard mill lengths, typically 12 m for 10M and 18 m for 15M and larger, as covered in our post on standard rebar lengths. Lengths available from a particular supplier can differ, so confirm them before you plan.

Waste comes from:

• Drops (offcuts). Whatever is left when the next piece no longer fits on the bar. A 5 m piece cut from an 18 m bar leaves 3 m after three pieces.
• Unusable short ends. Drops below the shortest piece you will ever need become scrap.
• Cutting each mark separately. The most common source. Each mark leaves its own drop, and they are rarely reused.
• Revisions. Bars cut to an old revision, or cut before a design change, become offcut stock or scrap.
• Miscuts and field cutting. Cutting on site from full lengths without a plan, then cutting again to fix a mistake. Our post on bending and cutting rebar on site covers when that makes sense.

Shearing rebar removes no material (unlike a saw cut, there is no kerf), so a well-planned stock bar can, in principle, be used to the last millimetre.

The basic idea: combine pieces across marks

Cutting optimization is a classic problem in operations research, usually called the one-dimensional cutting stock problem: given stock lengths and a list of required pieces, choose cutting patterns that use the fewest stock bars.

The rules that make it work for rebar:

1. Only combine the same bar size and grade. A 15M piece cannot come out of a 20M bar.
2. Work across the whole release. The more pieces you have of a size, the easier it is to fill gaps. Footings, walls and slabs poured together can be optimized together.
3. Use developed lengths for bent bars. An L-bar or stirrup is cut to its full developed length before bending. Get those from the cutting length formula, not the overall dimensions.
4. Respect the bar list. Optimization changes which stock bar a piece comes from, never the length of the piece. Lap lengths in particular are not shortened to fit a stock bar.

A worked example

A job needs these 15M pieces, cut from 18 m stock:

The total steel needed is 134.4 m, which is 7.47 stock bars, so the minimum possible is 8 bars.

Cutting each mark on its own:

• Mark A: three pieces per bar (15.6 m), leaving 2.4 m. Four bars, four 2.4 m drops.
• Mark B: five pieces per bar (exactly 18 m). Two bars, no drop.
• Mark C: seven pieces per bar (16.8 m), leaving 1.2 m. Fifteen pieces take three bars, the last with only one piece on it.

That is 9 stock bars and 27.6 m of offcut, spread over seven pieces.

Optimized: notice that each Mark A bar leaves exactly 2.4 m, the length of Mark C.

• Four bars cut 3 x A plus 1 x C each: no waste.
• Two bars cut 5 x B each: no waste.
• One bar cuts 7 x C, leaving 1.2 m.
• One bar cuts the last 4 x C, leaving an 8.4 m remnant.

That is 8 stock bars, the minimum possible, and the leftover steel is mostly in one 8.4 m remnant that can be used on the next order instead of seven separate drops. On a real job with dozens of marks per size, the same idea compounds.

Methods: by hand, Excel and software

By hand

For a handful of marks, look for lengths that add up to the stock length or close to it, as in the example. Pair long pieces with short ones that fill their drops.

Rebar cutting optimization in Excel

Excel works well for small lists:

1. List every piece of one bar size as a row, one row per piece, with its mark and length.
2. Sort from longest to shortest.
3. Fill stock bars in order. Put each piece on the first stock bar that still has room for it; open a new bar when none does. This is the "first fit decreasing" method, and it gets close to the best answer for typical bar lists.
4. Record the pattern for each stock bar, which becomes the cutting plan for the shear.

For a tighter result, the Solver add-in can choose how many times to cut each pattern (a combination of pieces that fits on one stock bar) to meet the quantities with the fewest bars. That takes more setting up and is rarely worth it for a small job.

Rebar cutting optimization software

Rebar detailing and fabrication software often includes cutting optimization: the bar list is grouped by size, combined with other orders being cut at the same time, and the shear receives cutting patterns directly. The software can also track remnants by size and length and use them first on later work. Standalone one-dimensional cutting optimizers, built for steel, pipe and lumber, can handle rebar too, as long as they work with bar sizes as separate materials.

Practical ways to cut waste on your job

Beyond the arithmetic, a few decisions upstream make the biggest difference:

• Order from a proper bar list. A fabricator can optimize across all the bars being cut. Buying full lengths and cutting on site throws that away. Our post on what a bar bending schedule is explains the document the shop works from.
• Settle splice locations early. Where the engineer allows a choice of lap locations, detailing bar lengths that suit the stock length (for example, a run of bars that divides evenly) reduces waste. The engineer decides where laps may go; see our lap splice length chart for the lengths involved.
• Group releases sensibly. Larger releases give more pieces to combine, but release too much too early and revisions can turn cut bars into scrap. Phased releases are a balance between the two.
• Standardize where you can. Fewer distinct lengths, for instance repeated dowel or tie sizes across footings, makes patterns easier to fill.
• Keep usable remnants, and decide what "usable" means. Set a minimum remnant length per size below which a drop is scrapped, so the yard does not fill with pieces that will never be used.
• Freeze revisions before cutting. The most wasteful bar is one cut to the wrong length.

None of this changes the structural design. Bar sizes, spacing, laps and cover come from the engineer's drawings; optimization only changes how efficiently the shop produces them.

Let us cut it from your bar list

We detail, cut, bend, tag and bundle rebar from 10M to 55M to your bar lists, so your crew receives the pieces they need, sorted by mark, without cutting from full lengths on site. Ask us about stock lengths and phased releases for your job. Send your drawings or bar list through our quote request, or see our rebar products.