The imperial quart is the quart of the British imperial system. It is one quarter of the imperial gallon, which NIST lists as exactly 4.54609 L, and equals 2 imperial pints or 40 imperial fluid ounces. The US liquid quart is smaller at 32 US fluid ounces.
Conversion
imperial qt = imperial gal ÷ 4
L = imperial qt × 1.13652
imperial fl oz = imperial qt × 40
Example
4.54609 ÷ 4 = 1.1365225 L. Forty imperial fluid ounces of 28.41306 mL give 1,136.52 mL as well. A US quart is 946.35 mL, so 1,136.52 ÷ 946.35 = 1.20: the imperial quart is about 20% larger, or 190 mL more.
Common mistakes
A 1 liter carton is smaller than an imperial quart (1,000 mL against 1,136.52 mL) but larger than a US quart (946.35 mL). See how many ounces in a quart for the US chart.