Metric vs. US Units: A Shopper’s Conversion Cheat Sheet

A useful shortcut: 100 g is about 3½ oz, and a kilogram is a little more than 2 pounds.

Shortcuts: a liter is a little more than a quart (33.8 vs. 32 fl oz), and a 330 mL can holds a bit less than a 12 fl oz can. UK (imperial) pints and gallons are larger than US ones — an imperial pint is 568 mL — but US measures are what US labels and this calculator use.

To convert a price, multiply or divide by the same factors — but the direction flips compared with sizes. A bigger unit means a bigger price per unit.

An imported 500 g pack of pasta costs $1.89. A US 16 oz box costs $1.79. Which is cheaper per ounce?

1. 500 g ÷ 28.35 ≈ 17.64 oz.
2. Imported pack: $1.89 ÷ 17.64 ≈ $0.107 per oz.
3. US box: $1.79 ÷ 16 ≈ $0.112 per oz.
4. The 500 g pack is about 4% cheaper, even though its shelf price is 10 cents higher.

One cheese is labeled $9.90 per kg, another $4.29 per lb. Convert the per-kg price: $9.90 ÷ 2.2046 ≈ $4.49 per lb. The per-lb cheese is about 4% cheaper. In the calculator you can skip the arithmetic: enter 1 kg for the first and 1 lb for the second, with their prices, and tap “per lb” or “per kg” to see both in the same unit.

• Enter each package in the unit printed on it — don’t convert in your head first. The calculator converts exactly.
• Weight converts to weight and volume to volume. Grams can’t be compared with milliliters, or ounces with fluid ounces — see ounces vs. fluid ounces.
• Pick the result unit that matches the shelf tags around you: per kg or per 100 g in metric countries, per lb or per oz in the US.
• Rounded label sizes can hide small differences: “1.1 lb” on a 500 g pack is rounded from 1.102 lb.

For everyday comparisons, the price per kg calculator, price per pound calculator and price per liter calculator open with the right units already selected.

A 1.5 L bottle of juice costs $2.49. A half gallon (64 fl oz) carton costs $2.29.

1. 1.5 L × 33.81 ≈ 50.7 fl oz.
2. Bottle: $2.49 ÷ 50.7 ≈ $0.049 per fl oz.
3. Carton: $2.29 ÷ 64 ≈ $0.036 per fl oz.
4. The half gallon is about 27% cheaper per fluid ounce — and it holds more, too.

Many US labels print both systems, for example “16 oz (453 g)” or “33.8 fl oz (1 L)”. The second number is usually rounded, so use the one printed as the main size when you can. The difference is tiny — 453 g vs. 453.6 g — and won’t change the winner unless two products are within a fraction of a percent of each other, in which case they are effectively the same price.

• Using 2 instead of 2.2046 to convert between kg and lb: $10.00 per kg is $4.54 per lb, not $5.00.
• Mixing UK and US pints or gallons.
• Comparing grams with milliliters — one is weight, the other volume.