Due to the beta state of this site and its use of English† only, most questions and answers use United States customary units, particularly inch and feet, but also gallons and degrees Fahrenheit (the latter already has been in question).
For the average US citizen that might be alright, but since they’re the only ones stuck in that ancient “system”, it’s always a hassle‡ converting to SI units.
I recently suggested such an approved revision and was about to do so again, but I think it’s a fundamental decision best determined on Meta.
Should US units always be supplemented by SI units?
- 20 ft x 3 ft (ca. 6×1 m)
- 1.5"-2" (3.81–5.08 cm)
- 20 gallon (about 75 liters)
- 100–110°F (~38-43°C)
† For non-native speakers, it’s notably harder in terms of gardening than, for instance, regarding computer science.
‡ It’s not just recognizing the physical quantity and converting the unit, but also rounding the result: An easy “100-110 °F” would be between 37.777… and 43.333… degrees centigrade, and obviously a notation of “38-43 °C” would be more than inaccurate.