Cross-Multiplication for Conversions

Converting units is a proportion problem. If 1 cup = 16 tablespoons and you need 2/3 cup, set up: 2/3 × 16 = 10.67 tablespoons (about 10 and 2/3). Cross-multiplication handles any conversion that's purely multiplicative — grams to ounces, milliliters to cups, metric to imperial. The exception is temperature: Celsius to Fahrenheit isn't a proportion, because it carries an added offset (F = C × 9/5 + 32), so you can't solve it by cross-multiplying alone.

The secret to painless kitchen math: memorize a few anchor conversions (1 cup = 240 mL, 1 oz = 28g, 1 inch = 2.54 cm) and derive everything else through proportions. With three or four anchors in memory, you can convert any recipe from any source.