Indium Blog

Do We in the US "Think Metric?"

  • Dr. Ron Lasky

  • 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.

    Some other approximations are helpful: 16​°C is about 61​°F, and -11​°C is about 11​°F.

    For much higher temperatures, degrees F is approximately 2 times degrees C. As an example 250​°C is close to 500​°F (actual 482​°F), 2000°C is about 4000​°F (actual 3632​°F). For values of degrees C above 1000​°C, if you subtract 10% of degrees F from itself, it gets you very close to the actual temperature. So, for 2000​°C, degrees F is very close to 2 * 2000 = 4000 - 0.1*4000 = 3600​°F, where the actual is 3632​°F.

    On my next post, I will discuss ways to convert metric to British distances and weights.


    Dr. Ron