I use following conversion factors:

1) For feet and inches:
1 foot = 30 cm
1 inch = 2,4 cm
20 feet 8 inches ~ 600 + 8*(2.5) = 620 cm


2) For pounds
- 165 lb ~ 82 kg (1/2) (easy)
(I don't remember the exact factor)


3) For mph:
- 45 mph ~ 67 km/h (1.5) (easy)
- 45 mph ~ 72 km/h (2*8/10) (a little more complicated)
And if it must be more accurate, I know in my head that 1 miles ~ 1.609 km


4) For °F:
- 85 °F ~ some where between 32°F (0°C) and 212°F (100°C) so maybe about 20°C ??? But if it must be more accurate, I could make the formula back from those values: F= C*(180/100) +32
Or C=(F-32)*(100/180)


5) alternatively, I go lazily to a conversion website if I am online...
Happily, I don't have to make this kind of calculations very often...except on AB!
For this reason, I usually use this last possibility.

I’m British, but unlike most Brits I can’t use the imperial system. Most Brits oppose the metric system because they get it confused with the EU. The rest of my family are exclusively imperial, yet I only understand metric (except for a yard because I know it’s nearly a metre).

If you said: “20 feet, 8 inches” I would have no idea; I wouldn’t even pause to work it out, I just wouldn’t know.

The same goes for 165 lb.

However, 45 mph I would understand because speed limits in Britain are in mph, but I prefer to think in km/h (speedometers in british cars are predominately mph, but must also show km/h). I know 50 mph is about 80 km/h, and 70 km/h is a little over 40 mph, so I would say it’s about 73 km/h.

Fahrenheit... absolutely no idea. Although here’s something to help you with °C:

30° is hot
20° is nice
10° is cold
0° is ice

When people ask how much I weigh I say: “82 kg”. When they ask what that is in imperial I’ll say: “6 tods, a clove and 6 pounds”. They’ll than ask what that is in stone so I tell them: “you’re the one who uses imperial measurements, you work it out”.

The only one I have difficulty with is when weight is expressed in pounds. I have to divide by 14 to convert it into stones, or 2.2 to convert it into kilograms.

We used feet and inches, and the Fahrenheit scale when I was at school.