\begin{definition}[Definition:Imperial/Volume/Gallon]
The '''(imperial) gallon''' is an imperial unit of volume.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''gallon'''
}}
{{eqn | r = 2
      | c = pottles
}}
{{eqn | r = 4 \cdotp 54609
      | c = litres
}}
{{eqn | r = 4 \, 546 \cdotp 09
      | c = millilitres
}}
{{end-eqn}}
\end{definition}