We use the metric system because it makes the math easier. You do not need to add and subtract fractions of a cup or or a teaspoon.
You need to be careful - but not fanatical - about measuring. Our chemicals are robust and small errors will not ruin your results.
FYI: 30 ml = 30 cc = 1 fluid ounce and 1000 ml = 1 liter = 1.06 quarts.
To convert metric measurements (ml) to American measurements (pints and quarts) click here