# Do We in the US "Think Metric?"

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• Folks,

I was reading BBC’s Science Focus Magazine when I came across a reader’s letter to the editor in the October issue on page 12:

“Reading the Q&A about fusion power (September p77),  I was struck by the fact that you gave temperatures in both Celsius and Fahrenheit. I’m pretty sure that all of your readers – even Americans – are familiar with Celsius and metric by now, or is there some benighted corner of the world where these systems are unknown?” - Alan Black

Well, my sense is that in the USA, most people are not familiar enough with Celsius and metric to make the conversions without a chart or app. Most of us don’t “think metric.” Years ago, being an engineer, I felt that I needed to make an effort, if not to think metric at least to get approximations in my head. So, the following are some of the tricks I use.

Room temperature of about 20°C is equal to 68​°F. Each 5​°C is equal to 9​°F. So, 25​°C is 77​°F or a pleasant day, 30​°C is 86​°F or a warm day, 35​°C is 95​°F or a hot day, and 40​°C is equal to 104​°F, a very hot day.

Going down from 20​°C, 15​°C is 68​°F minus 9​°F or 59​°F, and so forth. Most of us know that 0​°C is 32​°F, therefore -5​°C is 23​°F, etc. See the figure below for some help.

For really cold temperatures, -40​°C is -40​°F and you can use the 5​°C change is = 9​°F change for temperatures near -40​°C.