Inches and centimetres for the working kitchen.

Length comes up more often in the kitchen than people realise. Pan dimensions, dough thickness, slicing widths, knife sizes, the diameter of a tart ring, the width of a rolled-out sheet of pastry — all of these are length measurements, and recipes don't bother to translate between systems. American recipes use inches; most of the rest of the world uses centimetres or millimetres.

The conversion this tool uses

• 1 inch (in / ″) = 2.54 cm (exact, by international agreement since 1959)
• 1 centimetre (cm) = 0.3937 inches
• 1 metre (m) = 100 cm = 39.37 inches
• 1 foot (ft) = 12 inches = 30.48 cm

Pan dimensions you'll meet most often

• 6″ (15 cm) round — small layer cakes, tarts for two
• 8″ (20 cm) round — single-layer cakes, brownies in some recipes
• 9″ (23 cm) round — the standard layer cake size
• 10″ (25 cm) round — larger cakes, deep-dish pies
• 9 × 13″ (23 × 33 cm) — the universal sheet cake / casserole pan
• 8 × 8″ (20 × 20 cm) — brownies, small bakes
• 9 × 5″ (23 × 13 cm) — standard loaf pan

Mental conversions for the kitchen

For everyday estimation, two ratios cover almost everything you'll need: 1 inch ≈ 2.5 cm(it's really 2.54 — close enough for cookery) and 1 cm ≈ ⅜ inch. So a 9-inch pan is about 23 cm, a 12-inch pan is about 30 cm, and a 5-mm slice is about ¼ inch.

Length and pan substitution

When a recipe asks for a pan you don't have, length isn't the right comparison — areais. A 9-inch round pan has an area of about 64 in², not far off an 8-inch square (also 64 in²), so they're a clean substitute. A 9-inch round vs. a 9-inch square, however, are quite different (64 vs. 81 in²) and the swap will leave you with a thinner bake.

For pan substitutions by area rather than by linear dimension, use the pan-size converter. It calculates surface area for any round, square, or rectangular pan and tells you the capacity ratio of the swap.

Length, weight, and volume — when it matters

For most cooking, a millimetre or two of length difference is invisible. For thin pastry — puff pastry, rugelach dough, filo — the difference between 2 mm and 4 mm of thickness changes the bake noticeably. For knife work, “julienne” traditionally means matchsticks of 3 × 3 × 50 mm; “brunoise” means 3-mm cubes; “small dice” is closer to 6 mm. These conventions aren't arbitrary — uniform cuts cook uniformly.