The formula is simple:
Cost per gram (or ml) = ex-VAT pack price ÷ total grams (or ml) in the pack
Everything else in this article is about getting those two numbers right — because in UK foodservice, pack prices arrive with VAT, in cases, in litres, in "drained weight", and sometimes in dozens or bunches. Get the conversion wrong and every dish built on that ingredient carries the error forever.
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Most UK wholesalers (Bidfood, Brakes, local butchers, cash-and-carry) quote trade prices excluding VAT, but cash-and-carry receipts, supermarket prices and some online invoices are VAT-inclusive. Cost your recipes on ex-VAT prices — VAT you pay on ingredients is recoverable input tax if you're VAT registered, so including it inflates your food cost.
To remove standard-rate VAT (20%): ex-VAT = inc-VAT ÷ 1.2
Note that most unprocessed food is zero-rated in the UK anyway, so a lot of your grocery lines will have no VAT to strip. But hot food, confectionery, crisps, soft drinks, alcohol and many prepared items are standard-rated — as are non-food items like foil, gloves and takeaway packaging. Check the invoice rather than assuming.
Pick grams for everything solid and millilitres for everything liquid, and convert once. Common conversions you'll actually use:
| Supplier states | Base units |
|---|---|
| 1 kg | 1,000 g |
| 1 litre | 1,000 ml |
| 1 lb | 453.6 g |
| 1 oz | 28.35 g |
| 1 UK pint | 568 ml |
| 1 UK fl oz | 28.4 ml |
| 1 US cup (rare, US recipes) | ~240 ml |
| 1 gallon (UK) | 4,546 ml |
This is where most costing spreadsheets break. A case price is not a unit price.
Read the pack description carefully:
So a case of 6 × 2.5 kg plain flour at £14.40 ex-VAT is:
£14.40 ÷ 15,000 g = £0.00096 per gram (0.096p per gram, or £0.96 per kg)
A 500 g portion of that flour in a recipe costs 500 × 0.00096 = £0.48.
If your recipes only ever use one tub, decide whether you're costing at case rate or single-unit rate — buying the case is cheaper per gram, but only if you actually buy cases. Cost what you actually pay.
Three different numbers hide behind one tin:
A 2.5 kg tin of chickpeas might have a drained weight closer to 1.5 kg. If your recipe calls for 400 g of drained chickpeas, you must cost against the drained figure, or you'll understate the cost by a third. Same logic for tinned tuna in oil, jarred artichokes, mozzarella in whey, and anything packed in syrup.
If you use the liquid (chickpea water for hummus, tomato juice in a sauce), cost against net weight instead.
Cost per gram gives you the as-purchased (AP) cost. What your dish consumes is the edible portion (EP) cost.
EP cost per gram = AP cost per gram ÷ yield %
If a whole side of salmon costs £0.0180 per gram as purchased and you get a 65% yield after pin-boning, skinning and trimming, the usable flesh costs:
£0.0180 ÷ 0.65 = £0.0277 per gram — over 50% more than the invoice suggests.
The only reliable way to get your yield percentage is to weigh: record the as-purchased weight, prep it exactly as you normally would, then weigh the usable product. Do it three times and average. Your yields will differ from any published table because they depend on your knives, your specs and your standards.
Cooking loss matters too. If you cost a braised dish on raw weight but portion cooked, you need to know the cooked yield to portion accurately.
Some ingredients resist grams entirely. Two options:
Cost per unit. Eggs (per egg from the tray price), gelatine (per leaf from the box), tortillas (per wrap), pastry (per sheet). Divide pack price by unit count and use that as your base cost — no conversion needed.
Weigh a sample to create your own conversion. For a bunch of coriander, a bulb of garlic, or a lemon, weigh several and average. Now "1 bunch parsley" becomes "roughly 30 g of parsley" and you can cost it per gram like everything else — and scale it properly when you double a batch.
1 litre of water is 1,000 g. Almost nothing else in your kitchen is. Oil is roughly 0.92 g per ml, honey and glucose are well over 1.3, double cream and milk sit a little above 1.
If your supplier sells oil by the 20-litre drum and your recipes measure oil by weight, you need a density figure — or better, weigh a measured volume yourself. Pour 500 ml onto a scale, note the grams, and you have your own conversion factor for that exact product. Never assume "5 L = 5 kg".
Cost per gram is a tiny number. Round it to two decimal places and it becomes £0.00, which silently zeroes out your recipe. Store at least five or six decimal places, or work in pence per gram and cost per kilogram, which are easier to sanity-check by eye. Only round at the dish level.
A perfect conversion built on last spring's price list is still wrong. Practical habits:
Supplier line: Mature cheddar, 2 × 5 kg block, £53.60 ex-VAT
Recipe line: 80 g grated cheddar per portion, grating yield 96% (rind and losses)
1. Total grams: 2 × 5,000 = 10,000 g
2. AP cost per gram: £53.60 ÷ 10,000 = £0.005360
3. EP cost per gram: £0.005360 ÷ 0.96 = £0.005583
4. Portion cost: 80 × £0.005583 = £0.4467 ≈ 45p
That's a defensible number you can build a menu price on.
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Doing this by hand for 40 ingredients across 25 dishes is where most kitchens give up — and where margins quietly disappear. If you'd rather get the numbers without the spreadsheet gymnastics, run a dish through the free food cost calculator at getprepsheet.com/calculator, or pick up a ready-made Excel costing template from the PrepSheet shop with the pack-size conversions, yields and portion maths already built in.