Convert Celsius to Fahrenheit in your head
Double it, knock off a tenth, add 32. That's the exact formula, just in friendly pieces.
- Take the Celsius temperature, like 25°C.
- Double it: 50.
- Subtract a tenth of that: 50 − 5 = 45.
- Add 32: 77°F.
Tip: Going the other way? Subtract 32, then multiply by 5/9: (68 − 32) × 5/9 = 20°C.
Try it now: Convert 30°C and 15°C. (86°F and 59°F.) Then check: 100°C should give 212°F.
Next crumbs
- 🧮 Mental mathSwap a percentage to make it easy8% of 25 is hard. 25% of 8 is easy, and it's the same number.
- 🧮 Mental mathWork out a tip in your headMove the decimal point once, then double it or add half.
- 🧮 Mental mathTell if a number divides by 3Add up the digits. If that sum divides by 3, so does the whole number, however long it is.