While these conversions are not 100% mathematically correct, the simplified equations will work in most recipes.
See also Simple Weight Measures

1/8 teaspoon = 0.5 milliliters

1/4 teaspoon = 1 milliliter

1/2 teaspoon = 2.5 milliliters

3/4 teaspoon = 4 milliliters

1 teaspoon = 5 milliliters

1 1/4 teaspoons = 6 milliliters

1 1/2 teaspoons = 7.5 milliliters

1 3/4 teaspoons = 8.5 milliliters

2 teaspoons = 10 milliliters

1/2 tablespoon = 7.5 milliliters

1 tablespoon (3 teaspoons, 1/2 fluid ounce) = 15 milliliters

2 tablespoons (1 fluid ounce) = 30 milliliters

1/4 cup (4 tablespoons) = 60 milliliters

1/3 cup = 90 milliliters

1/2 cup (4 fluid ounces) = 125 milliliters

2/3 cup = 160 milliliters

3/4 cup (6 fluid ounces) = 180 milliliters

1 cup (16 tablespoons, 8 fluid ounces) = 250 milliliters

1 1/4 cups = 300 milliliters

1 1/2 cups (12 fluid ounces) = 360 milliliters

1 2/3 cups = 400 milliliters

2 cups (1 pint) = 500 Milliliters

3 cups = 700 Milliliters

4 cups (1 quart) = 950 milliliters

1 quart plus 1/4 cup = 1 liter

4 quarts (1 gallon) = 3.8 liters