I live in the American South, and I’m happy to wear shorts outside at 10C (50 F), so long as it’s not windy…

Now, a jacket at 30C (86F)… that’s a bit warm for me…

F = C*(9/5)+32

If you don’t want the ratio, 9/5=1.8

To estimate the temperature conversion, multiply by 2 and add 32… then estimate a touch less… I eyeballed 10C to be 50ish before breaking out the calculator and finding it was 50 on the nose