A quart is a unit of measurement for volume. It is equal to two pints. There are several different units known as a pint, and so there are accordingly several different quarts.
  • US liquid measure:
    • equal to two US liquid pints
    • defined as one quarter of a US gallon
    • equal to 32 US fluid ounces
    • equal to 0.946352 litres

  • US dry measure ("dry quart"):
    • equal to two US dry pints
    • defined as 1/32 of a US bushel
    • equal to 67.2 cubic inches
    • equal to 1.101220 litres
In imperial (UK & Canadian) measure a quart is a measure of capacity, liquid or dry
  • Imperial measure:
    • equal to two imperial pints
    • defined as one quarter of an imperial gallon
    • equal to 40 imperial fluid ounces
    • equal to 1.1365225 litres exactly

Reference

[http://physics.nist.gov/Document/sp811.pdf Guide for the Use of the International System of Units (SI)] US government publication; includes US-(liquid)-to-litre & imperial-to-litre conversion