Compare unit prices:
multipacks, sizes and subscriptions.

Start with one denominator

How do you calculate unit price?

Unit price = item price / total quantity. For price per 100 g, divide by the grams and multiply by 100. The ACCC's unit-pricing explanation covers comparison by weight, volume, length, area or count.

Convert both offers first: 1 kg is 1,000 g; 1 litre is 1,000 ml. Compare matching products and variants on the same tax and currency basis. Arithmetic does not establish equal quality or performance.

Fictional example

Multiply every pack before dividing the price.

Assume these are the same dry pasta in different pack sizes, available under identical purchase conditions.

Check what one use means

Concentrates and servings need another check.

Suppose a fictional $6, 1-litre cleaner specifies 50 ml per use: 20 uses at $0.30 each. A $6.75, 750 ml concentrate specifies 25 ml: 30 uses at $0.225 each. The concentrate has the higher price per litre but the lower price per stated use.

That comparison assumes equal suitability and results under matching conditions. It is a comparison of alternatives, not proof that different formulas are identical. Use the actual label instructions; never invent a smaller dose to improve the arithmetic.

Likewise, check the grams behind a food's serving count. The FDA explains that a US Nutrition Facts serving size describes customary consumption, not how much you should eat. Two '20-serving' packs need not contain equal quantities.

One-off or recurring?

Do not extend an introductory price into the future.

Imagine identical 40-count packs: $10 for a one-off purchase, versus $8 for the first subscription delivery and $11 for the next. With two deliveries at those assumed prices, the subscription costs $19 for 80 pieces, or $0.2375 each. Two one-off packs cost $20, or $0.25 each. The first delivery's 20% item saving becomes 5% across the pair.

Keep these as separate purchase scenarios. Verify recurring charges, minimum deliveries, cancellation timing, coupon eligibility and membership fees. Future prices may change. The FTC's subscription guidance recommends checking terms and renewal prices. A member fee belongs in your spending decision, separately from item-price ranking. For sale-specific preparation, see our Prime Big Deal Days guide.

Resolve these before ranking

Small labels can change the calculation.

A repeatable comparison

Check two offers before choosing a pack.

Allow about five minutes when the labels are clear. Missing information can take longer to resolve.

After the arithmetic

Choose a quantity you can use.

A lower verified unit price does not require you to buy more. Check storage, budget and likely consumption. The EPA recommends planning quantities to avoid overbuying food. Keep that personal buying decision separate from the calculated price ranking.