Knowing how to make conversions between different units of weight measurement can be a very good skill to have in the kitchen. For example, it can allow you to use recipes created in the metric system, where weights are given in grams, a form more familiar to U.S. cooks who normally measure ingredients in weight ounces. Another type of conversion occurs if you want to change the overall quantity of the recipe—to make half as much or twice as much, for example.
This can be further complicated if you are doing both types of conversion—changing from metric to imperial measurements (or vice versa) plus changing the overall quanities. Making the correct conversions can make or break your final results.
Imperial and Metric Equivalents
It doesn't take sophisticated math skills to make simple imperial-to-metric conversions, provided you understand the basic equivalencies. Any number of tables are available to do this, or you can use a simple online conversion app. Smartphones also have convenient conversion apps available.
The rudimentary conversions include:
- 1 ounce = 28 grams
- 1 pound = 16 ounces
- 1 pound = approximately 1/2 kilogram
- 1 kilogram = 1,000 grams
- 1 kilogram = 2.2 pounds
For example, if you want to convert a recipe developed in Europe to quantities more familiar to U.S. cooks, converting gram measurements to ounces is simply a matter of dividing the gram measurement by 28.
For example, if an ingredient calls for 21 grams, divide by 28 to arrive at 3/4 (.75) ounce. Similarly, a European cook could deduce that the 4 ounces of cheddar cheese called for in an American recipe translates as 112 grams (4 x 28).
Quantities by Weight vs. Quantities by Volume
Most recipes in the United States measure ingredients by volume rather than weight, while elsewhere in the world, it's more common for ingredients to be listed by metric weight.
For example, a recipe developed in a U.S. test kitchen might call for 3 tablespoons of butter, while a similar recipe from Europe might list this quantity as 40 grams. For this reason, it's a good idea for anyone who does a lot of cooking to own a good metric kitchen scale in order to make use of any recipe you might come across. While it is possible to convert metric quantities to volume quantities for most ingredients, you'll find yourself looking up individual ingredients frequently. Here are some of the conversions for regularly used ingredients:
- Unbleached all-purpose flour: 1 cup = 4 1/4 ounces = 120 grams
- Self-rising flour: 1 cup = 4 ounces = 113 grams
- Baking powder: 1 teaspoon = 4 grams
- Baking soda: 1/2 teaspoon = 3 grams
- Butter: 1/2 cup =1 stick = 4 ounces = 113 grams
- Sugar (granulated white): 1 cup = 7 ounces = 198 grams
A number of online tools are available for other ingredients that are often measured by volume.
Measuring ingredients by weight is generally a better, more accurate method than measuring by volume, especially with ingredients like flour, which often may become compacted during storage.
Converting Overall Recipe Quantities
Another type of conversion comes when you are changing the quantity of the recipe—making a recipe with half as many, or twice as many portions.
This is pretty basic arithmetic involving simple multiplication. If you want to make half as much, then each ingredient quantity is divided by 2 (or multiply by 0.5). To double a recipe quantity, you will multiply each ingredient quantity by 2.
Changing overall quantities is equally simple whether you're working from a recipe with imperial measurements, where the ingredients are measured by ounces or by volumes, or a metric recipe where all ingredients are measured in weight by grams. It's a matter of adjusting the quantities of the individual ingredients by the same proportions that the overall recipe quantities are being adjusted.
If you are doing both conversions—metric to imperial, as well as changing the overall quantity of the recipe, just make sure to carefully do the unit conversions before you do the overall quantity adjustment.
Measuring Weight in the Kitchen
A kitchen scale is necessary to measure ingredients by weight. It is well worth the investment of a few dollars to buy a good scale that will ensure you are getting the right measurements for your recipes. Measurements are critical for baking, for example. It can mean the difference between a beautiful loaf of bread and a sad lump of hardened dough. Other recipes may be more forgiving and you can adjust them by taste. But better to start off in the right ballpark by measuring.
A good digital scale can be set to read either in ounces or grams, making it perfect for any recipe you might prepare. Kitchen scales are precision tools designed to measure accurately in the small increments of weight used in many recipes. Most general-purpose postal scales are not accurate enough for kitchen use.
When using a kitchen scale, it's common practice to weigh a vessel that you will put the ingredients in, then "zero" the scale so its weight is not included. Then you can place your ingredient in the vessel, such as a cup, and the scale will show the net weight on the ingredient only.
Weight Ounces vs. Volume Ounces
It is important to remember that the term "ounce" is used both as a unit of weight measurement as well as a unit of volume. Dry ingredients such as beans, flour, and sugar are often measured in weight ounces, while liquids and other wet ingredients are often measured in volume or fluid ounces.
On packaged goods, weight ounces are listed as "NET WT OZ’," where WT stands for weight; while volume ounces are listed as "NET OZ FL," where FL stands for fluid. When an ingredient calls for OZ FL, do not make the mistake of measuring it by weight on a scale, but rather by using a graduated measuring cup marked in fluid ounces.