KaelSite
Contact us Sign in

Reduce Material Waste

Cutting List Calculator: How to Reduce Steel, Timber and Pipe Waste on Site

Buying and cutting standard-length materials without a plan means more waste and more cost. Learn how a cutting list works, what kerf is, and how to work out the fewest stock lengths you need, with a worked example and a free calculator.

Last updated 7 November 2026

Why cutting plans matter on site

Steel bar, timber, pipe and conduit are sold in fixed lengths, but the pieces you need rarely match them. If each length is cut as it is needed, you end up with short offcuts that nobody uses, extra deliveries, and a skip filling up with material you paid for.

A cutting list fixes this before anyone picks up a saw. It decides which pieces come out of which stock length, so you buy fewer lengths and waste less. KaelSite’s free Material Cutting Optimiser does this for you.

How the calculation works

The task is known as the one-dimensional cutting stock problem. You have stock lengths of a fixed size, a list of required lengths with quantities, and you want the fewest stock lengths that cover everything. In practice, three inputs matter:

  • Stock length: the length you buy, for example 6,000 mm for a steel bar or 4,800 mm for timber.
  • Kerf: the material removed by each cut. A saw blade can take 2 to 5 mm every time, and it adds up over many pieces.
  • Minimum reusable offcut: the shortest leftover you would keep. Anything shorter counts as scrap.

A quick estimate is to add up all the required lengths including kerf and divide by the stock length. This gives a minimum, but you can rarely reach it, because pieces have to fit whole onto a bar. The real answer comes from combining different lengths on the same bar.

Worked example

A site needs the following from 6,000 mm bars, with a 3 mm kerf:

Piece Length Quantity
A 2,400 mm 6
B 1,800 mm 4
C 1,200 mm 8

Each cut uses its length plus 3 mm of kerf, so the total is 31,254 mm. Divided by 6,000 mm, that is 5.2 bars, so the best case is 6 bars.

Cutting one length at a time needs 7 bars: 3 bars for A (two per bar), 2 for B (three per bar, then one) and 2 for C (four per bar).

A planned cutting list needs 6 bars:

  • 4 bars each with 1 × A, 1 × B and 1 × C (5,409 mm used, 591 mm left)
  • 1 bar with 2 × A (4,806 mm used, 1,194 mm left)
  • 1 bar with 4 × C (4,812 mm used, 1,188 mm left)

That is one bar saved, and the leftovers are 591 mm, 1,194 mm and 1,188 mm. If your minimum reusable offcut is 500 mm, all of them can be kept for another job rather than scrapped. The pieces cut total 31,200 mm out of 36,000 mm bought, about 87% used.

Common mistakes

  • Forgetting kerf. Cutting six 1,000 mm pieces from a 6,000 mm bar leaves you short because of the blade width.
  • Cutting one size at a time. This leaves awkward offcuts that fit nothing else on the job.
  • Ignoring offcuts already on site. Check what you have before ordering new stock.
  • Mixing units. Entering metres in one field and millimetres in another gives wildly wrong results. Pick one unit and check it.
  • Not allowing for trimming. Rough or damaged bar ends may need cutting off first, so reduce the stock length to match what is usable.

Works for more than steel

The maths is the same for any linear material sold in fixed lengths, including steel bar and sections, timber, aluminium, pipe and conduit. Set the stock length and kerf for your material and enter the cuts.

Waste, cost and compliance

Less offcut waste means lower material and disposal costs, and it supports the waste hierarchy that applies to construction waste in England and Wales, where preventing waste comes first. A cutting list also gives your team a clear instruction, so the right pieces get cut the first time.

How good is the result?

The KaelSite optimiser tells you whether the answer is proven to use the minimum number of stock lengths or is a strong heuristic result. For smaller jobs it can prove the minimum. For larger ones it uses a well-established method and says so, so you know what you are getting.

Frequently asked questions

How do I calculate how many steel bars I need?
Add up every required length including kerf and divide by the stock length for a rough minimum. For a reliable number, enter your lengths and quantities into a cutting list calculator, which fits pieces onto bars properly.

What is a good kerf allowance?
It depends on the blade or cutting method. Check your saw blade’s thickness. Many cuts on steel or timber take roughly 2 to 5 mm, but use your own figure.

Can I include offcuts I already have?
Yes. Enter the lengths available and the optimiser tries them before buying new stock.

Does it work for timber and pipes?
Yes, for any material sold in fixed lengths.

Related calculators

Planning materials usually involves more than one calculation. These tools work well alongside the cutting optimiser:

See all of them in our complete guide to free construction calculators.

Keep your site records in one place

Material planning is one part of running a site. KaelSite helps UK site teams manage inspections, safety and reporting from one mobile-first app. Explore KaelSite features.

References