Definition
Gallon
A gallon is a capacity unit whose size depends on the measurement system.
Continue from this idea into connected AXIO math.
What it means
A gallon tells how much a container can hold, but the word needs a system name. US and imperial gallons are different sizes, so find the system before comparing or converting.
Remember it
Give every gallon a name tag: US or imperial.
Example
A US container holds 2 gallons. Since 1 US gallon is 4 US quarts, it holds 2 × 4 = 8 US quarts.
Watch for
An unlabelled gallon is not enough information for an exact conversion because US and imperial gallons differ.
Common mix-up
Do not use the imperial value for a US gallon: 4.54609 L is imperial, not US.
Exact meaning
A gallon is a unit of capacity. One US liquid gallon equals exactly 231 cubic inches (3.785411784 litres); one imperial gallon equals exactly 4.54609 litres.