Everyday Money
Cost Per 100g Calculator
Normalise any pack price to a cost per 100 grams so different sizes are comparable.
Why compare per 100g?
Shelf stickers are not always in the same unit. Reducing everything to cost per 100g shows whether a bigger pack is actually cheaper — a habit that pays off in the cereal aisle, the butcher’s counter and online grocery. Enter pack price and grams; the calculator scales to 100g so awkward sizes (375g, 1.25kg) become comparable. It does not account for waste, quality, bone-in versus boneless, or shipping. For liquids use cost per 100ml; for two offers at once use unit price comparison. Drained weight on tinned goods is the fairer denominator when brine is half the label weight. Butchers and deli counters often price per kilogram while pre-packs show a total — convert both before comparing. When cooking loss is high (bacon, joint shrinkage), price the edible yield rather than the raw pack weight if you want a plate-level view.
Worked example
A 500g pack of pasta at £1.10 is £0.22 per 100g. A 1kg pack at £1.90 is £0.19 per 100g. You save 3p per 100g on the larger bag — £0.30 on a kilo — if you will finish it before it goes stale.
Limits and assumptions
Promotional multibuy prices need the effective pack price after the deal. Loyalty-card prices apply only if you will scan the card. Premium brands may cost more per 100g and still be the right buy for taste or ingredients. Organic, Fairtrade or higher-welfare premiums will lose a pure unit-price contest and may still be the purchase you want.
Frequently asked questions
Why use per 100g instead of per kg?
UK shelf labels often quote per 100g. Either scale works; multiply per 100g by 10 for per kg.
How do I handle ‘drained weight’ tins?
Use drained grams when comparing edible contents. Label weight includes liquid you may discard.
Does this work for meat with bone?
Compare like with like. Bone-in per 100g looks cheaper until you price edible yield.
What if one pack is on a multibuy?
Enter total spend divided by total grams across the deal packs.
Can I compare loose and pre-packed?
Yes — weigh a typical loose portion or use the ticket weight, then compare per 100g the same way.