To compare supplier prices properly, you have to convert every price to the same unit, a true cost per unit, because suppliers quote the same product in different pack sizes, descriptions and codes, and until you strip all of that away the cheapest-looking price is often not the cheapest. One supplier prices per box, another per case, a third per pallet, a fourth per item, and your eye cannot reconcile them. This guide explains why comparing supplier prices is so much harder than it should be, what "like for like" actually means, and how to normalise prices to a true unit cost so you can see who is genuinely cheapest.
It applies to any business that buys the same things regularly from more than one supplier, whether you are in manufacturing, construction, wholesale, logistics or hospitality.
Why is it so hard to compare supplier prices?
Because no two suppliers describe or package a product the same way. The item is identical, but everything around the price is different. One quotes a box of 100, another a case of 1,000, another a single unit. One uses the manufacturer's name, another an internal code, another an abbreviation only they understand. Pack sizes, units of measure, minimum orders and delivery terms all vary. So when you lay three quotes side by side, you are not comparing prices at all, you are comparing packaging. The headline number that looks cheapest may be dearest once you work out what you are actually getting for it.
This is why "just get three quotes" so often fails to save money. The quotes arrive in three different shapes, nobody has time to convert them, and the order ends up with whoever is easiest or most familiar.
What does "like for like" actually mean?
It means two things at once: the same product, and the same unit. You have to be sure you are comparing the identical item, with the same grade and spec, and you have to express every price in one common unit so the numbers are directly comparable. Get either wrong and the comparison is worthless. A lower price for a thinner glove, a shorter roll or a lower board grade is not a saving, it is a downgrade. A lower price per box means little when the boxes hold different quantities.
Like for like is the discipline of removing every difference except the one that matters: what the same thing actually costs you.
How do you normalise prices to a true unit cost?
Normalising just means reducing every quote to one comparable number. By hand, the method is:
- Confirm it is the same product. Check the spec, grade and size match, whatever the name says. Different words, same item.
- Pick one common unit. Per item, per litre, per kilo, per metre, whatever makes sense for that product. Use the same unit for every supplier.
- Convert each price to that unit. Divide the pack price by the number of units in the pack. A £46 case of 1,000 is 4.6p each; a £4.95 box of 100 is 4.95p each.
- Line them up and compare. Now, and only now, the cheapest number is genuinely the cheapest price.
It is simple arithmetic. The hard part is doing it reliably across dozens of products and suppliers without slipping up, which is exactly where it tends to fall apart.
Unit price is only part of the picture. The full comparison also accounts for landed cost, such as delivery charges, along with minimum order quantities and payment terms. A lower unit price that carries a delivery charge or a large minimum order may not be the cheaper option.
A worked example: four prices for the same item
Take a box of disposable nitrile gloves, something almost every business buys, quoted by four suppliers.
| Supplier | How they quote it | Headline price | True cost per glove |
|---|---|---|---|
| Supplier A | Case of 1,000 | £46.00 per case | 4.6p |
| Supplier B | Box of 200 | £9.60 per box | 4.8p |
| Supplier C | Box of 100 | £4.95 per box | 4.95p |
| Supplier D | Priced per glove | 5.2p each | 5.2p |
Glance at the headline column and Supplier D looks cheapest, because 5.2p sits next to prices in pounds for everyone else. Normalise to the cost per glove and the order flips. Supplier D is the dearest, and Supplier A, with the biggest headline number at £46.00, is the best value. The dearest option costs around 13% more than the cheapest for the identical glove. (Illustrative figures.)
The same trap turns up in other sectors. With cleaning concentrate, the dilution rate decides the real cost.
| Product | Pack price | Dilution | Usable solution | Cost per usable litre |
|---|---|---|---|---|
| Brand X | £12.00 for 5 litres | 1:20 | 105 litres | About 11.4p |
| Brand Y | £18.00 for 5 litres | 1:50 | 255 litres | About 7.1p |
Brand X looks cheaper by £6 a container, yet it costs about 60% more per usable litre. (Illustrative figures.)
Now multiply that confusion across every product you buy, and you can see how overpaying becomes the default rather than the exception.
Why does this matter beyond a single comparison?
The same problem scales, and it compounds. A business buying a few hundred products from twenty-odd suppliers makes hundreds of comparisons, every one of them obscured by mismatched units and descriptions. Nobody has the hours to normalise all of that by hand, so it never gets done, and small overpayments on line after line quietly add up to a large number over a year.
Normalisation is also the foundation of two things that save real money. You cannot build a fair supplier tender without it, because suppliers have to be compared on a level field. And you cannot build a proper spend analysis without it, because a year of spend only becomes useful once the same product is recognised as one line wherever it appears. Get the comparison right and everything downstream gets easier.
How do you do this across a whole year of invoices?
This is the point where doing it by hand stops being realistic and software earns its place. Purchasing Portal reads every supplier invoice, recognises the same product across different suppliers, codes and pack sizes, and converts every price to one comparable unit automatically, so a year of messy invoices collapses into a clean list showing exactly what you pay per unit and who charges what. You review and confirm the matches, so you stay in control, but the tedious normalisation is done for you.
From there you can see your real prices, take the gaps to a tender, and hold suppliers to the result. If you would rather not run any of it yourself, the team at Parallel Purchasing does the whole thing for you and is paid from the savings delivered.
FAQ
What does "cost per unit" mean?
It is the price of a product reduced to a single, consistent unit, per item, per litre, per kilo or per metre, so that quotes in different pack sizes can be compared directly. It is the only fair basis for comparing suppliers.
Why can't I just compare the prices on the quotes?
Suppliers quote in different pack sizes, units and descriptions, so the headline prices are not comparable. Once you convert everything to the same unit, the one that looked cheapest often turns out to be dearer.
Does this only matter for big spenders?
No. Any business buying the same items regularly from more than one supplier is exposed, whatever the size. The saving is a percentage of ongoing spend, so even modest volumes add up over a year.
What if the products are not quite identical?
Then you are no longer comparing like for like. Match the spec, grade and size first. A cheaper price for a lower specification is a different decision, and you should weigh it on its own terms.
Seeing what you actually pay, per unit, across every supplier is the first move in paying less. Book a demo and we will show you, on a few of your own invoices, what a normalised price list looks like.
See your prices normalised to a true cost per unit.
Book a demo →Matt Armitage runs Parallel Purchasing, a procurement consultancy for UK food and bakery SMEs, and built Purchasing Portal to put the same analysis in owner-managers' hands.