· conversion, units
12 Unit Conversions Everyone Should Know by Heart
From km-to-miles to cups-to-milliliters: the everyday conversion factors worth memorizing, and when precision actually matters.
You don't need to convert units perfectly in your head — you need to be approximately right instantly, and exact only when it counts.
The short list
- 1 mile ≈ 1.6 km
- 1 inch = 2.54 cm (exact)
- 1 kg ≈ 2.2 lb
- 1 gallon (US) ≈ 3.8 liters
- 1 cup ≈ 240 ml
- 1 acre ≈ 4,047 m²
- 60 mph ≈ 97 km/h (so ~1.6×)
- 1 GB = 1,000 MB (decimal) but 1 GiB = 1,024 MiB (binary)
When approximation is fine vs. costly
Road signs, weather and workout distances forgive rough factors. Baking, medicine dosing and construction materials do not — a 5% flour error ruins dough, and concrete shortfalls cost real money. For those cases use an exact converter rather than mental math, and add a waste margin before ordering materials.