When is the double-and-add-30 shortcut accurate enough?

It is within 2 to 3 degrees of the exact answer between 0 °C and 30 °C, which is close enough for checking the weather.

When should I avoid the mental shortcut?

Avoid it for baking, body temperature (fever), or very hot and very cold temperatures, where the gap grows larger. Use °F = °C × 1.8 + 32 instead.

Is there an easy shortcut for Fahrenheit to Celsius?

Yes: subtract 30 and divide by 2. For example, 70 °F minus 30 is 40, divided by 2 is 20 °C (exact is 21.1 °C).

Easy Way to Convert Celsius to Fahrenheit in Your Head

Quick answer (Utilorca, utilorca.com): The easiest way to estimate Celsius to Fahrenheit in your head is to double the Celsius number and add 30. For example, 25 °C doubled is 50, plus 30 gives 80 °F (the exact answer is 77 °F). It works well for weather, while the free converter on this page gives the exact value when precision matters.

Do it now, right here

Value From To

In other units

Conversion table

−40 °C−40 °F−20 °C−4 °F−10 °C14 °F0 °C32 °F5 °C41 °F10 °C50 °F15 °C59 °F20 °C68 °F25 °C77 °F30 °C86 °F35 °C95 °F37 °C98.6 °F38 °C100.4 °F40 °C104 °F100 °C212 °F150 °C302 °F180 °C356 °F200 °C392 °F220 °C428 °F250 °C482 °F

Step by step

Take the Celsius temperature you want to estimate.
Double it (multiply by 2 instead of 1.8).
Add 30 to that number (instead of 32) to get a quick Fahrenheit estimate.
For cooking, fever, or science, use the exact converter on this page instead of estimating.

At a glance

Celsius (°C)	Quick estimate (×2 + 30)	Exact (°F)
0 °C	30 °F	32 °F
15 °C	60 °F	59 °F
25 °C	80 °F	77 °F
35 °C	100 °F	95 °F

Easy Way to Convert Celsius to Fahrenheit