Gangsaw recovery: the maths of cutting

Ask a processor what their gangsaw recovery is, and most can't tell you — not because they don't care, but because the number lives nowhere. Yet it may be the most important figure in the whole business, because cutting is exactly where a yard's margin is made or lost.

Recovery and wastage, defined

When a block goes into the gangsaw, some of it becomes usable slab and some is lost to the cut. Two numbers describe what happened:

• Recovery % = slab area produced ÷ block area consumed × 100
• Wastage = block area consumed − slab area produced

If you feed 100 sqft of block into the saw and get 68 sqft of slab out, your recovery is 68% and your wastage is 32 sqft. That wastage isn't free — you paid for the whole block. So the cost of those 32 lost square feet has to go somewhere.

Where the money leaks

Here's the mistake almost every paper-run yard makes: they price slabs off the block's nominal cost per square foot.

Say a block cost ₹40,000 for 100 sqft — ₹400 per sqft. It's tempting to price the slabs as if they cost ₹400 per sqft. But you only got 68 sqft of slab. The real cost of the surviving slabs is:

true slab cost per sqft = block cost ÷ slab area produced = ₹40,000 ÷ 68 = ₹588 per sqft

Nearly ₹190 per square foot higher than the nominal figure — and if you quote off the nominal number, every one of those slabs is being sold with a chunk of your margin already gone, invisibly, before you even negotiate.

Wastage has to be priced in

This is the whole point: the cost of the wastage must land on the slabs that survived. The block's entire material cost gets spread over the actual output, not the theoretical output. A low-recovery cut makes each surviving slab genuinely more expensive — and a yard that prices honestly protects its margin, while a yard that prices off nominal cost slowly gives it away.

Recovery-adjusted costing does this automatically: it takes the block's cost, divides it across what actually came off the saw, and every slab carries its true cost from that moment. Where the cost is genuinely unknown, it should show as unknown — never faked into a rosy margin.

The leftover is not scrap

One more thing the maths should capture: the part of the block that wasn't consumed. If you cut 60 sqft out of a 100 sqft block, the remaining 40 sqft still has value — it's a smaller block, sellable to a different buyer. Track it as a remnant, and offcuts stop being losses and start being inventory.

Why tracking it changes behaviour

The moment recovery is measured on every cut, two things happen. Low-recovery blocks and low-recovery operators become visible — you can see which stone and which practices waste material. And your quotes finally rest on true cost, so you stop accidentally selling below it.

You don't need software to do this maths — you need to do it at all. Most yards don't, because doing it by hand on every cut is impractical. That's the gap worth closing, however you close it: recovery is only useful if it's measured every single time, not estimated once a year.