Helpful Conversions

In cooking and baking, different measurements are used depending on the source you are using. These measurements refer to ingredient amounts, pan sizes, and temperatures, and can be metric or imperial, or by dimensions or volume. All of these conversions are merely approximations and rounded values. It is recommended that when cooking and baking, you refer to the same set of measures for everything in the recipe, as the equivalents are not exactly equal, but if you use all of the same measurement for your recipe, it will turn out, whether you are using metric measurements or imperial. For example, use all imperial measures, do not measure some ingredients imperially and some ingredients metrically.

Oven Temperatures: Fahrenheit to Celsius to Gas Mark
300◦F = 150◦C = 2 (very low)
325◦F = 160◦C = 3 (low)
350◦F = 180◦C = 4 (moderate)
375◦F = 190◦C = 5 (moderate)
400◦F = 200◦C = 6 (hot)
425◦F = 220◦C = 7 (hot)

Baking Pan Measures: Imperial to Metric to Volume
8 inch square = 20 cm square = 2 L
9 inch square = 23 cm square = 2.5 L
8 inch round = 20 cm round = 1.2 L
9 inch round = 23 cm round = 1.5 L
9x13x2 inch rectangle = 21x33x5 cm rectangle = 3.5 L
10x15x1 inch jelly roll = 25x40x2 cm jelly roll = 2 L
9x5x3 inch loaf pan = 23x13x7 cm loaf pan = 2 L

Ingredient Measures: Imperial to Metric
1 cup = 250 mL
1/2 cup = 125 mL
1/3 cup = 80 mL
1/4 cup = 60 mL
1 Tbsp = 15 mL
1 tsp = 5 ml
1/2 tsp = 2 mL

Weights
1/2 ounce = 14 grams
1 ounce = 29 grams
2 ounces = 57 grams
4 ounces = 113 grams
8 ounces = 227 grams
16 ounces = 454 grams (one pound)

As you can see above, eight ounces is equal to approximately 227 grams. However, we generally say that one cup (250 mL) is equal to eight ounces, and that grams and milliliters are equal in weight. This shows that these measurement conversions are not precise. Also note that I did not list the conversion of measurements to exact weights (which is considered the most accurate way to measure ingredients correctly), because every ingredient has a different density - that is the weight of the ingredient compared to the amount of it, so every item would need a different conversion.
I have come to be familiar with many of these conversions over the years, but I did not memorize all of them. Some I had to look up on some of my handy charts and guides. These guides are commonly found in cookbooks, on the internet, and even in individual recipes.
PHOTO CREDIT: "cuisipro_stainlesssteel..." http://sweetkd.wordpress.com/2011/03/02/to-weigh-or-not-to-weigh-that-is-the-question.Cooking Therapy, n.d. Saturday, November 19, 2011