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Converting Units

A Short Guide

Converting between units is a very important skill in our day to day soapmaking activities. We work with converting weight to different units, converting weight to volume, converting temperature from Fahrenheit to Celsius, and converting SAP values of fats to calculate the correct amount of lye to add.

Converting between units is straightforward as long as you think of it as physically measuring something. For instance, weigh out 1 pound of coconut oil. Now think “that 1 lb is the same weight as 454 grams”. Weigh out 1000 grams of olive oil. Now think “that 1000 grams of oil is the same weight as 1 kilogram and as 2.2 pounds”.

Out of these physical relationships, you will understand the ratios and how to use them in calculations.

Here are some common conversion ratios that will be necessary to know for the Basic Soapmaker Certification tests. As we work in a diverse world, we need to know how to convert between English units (pounds and ounces) and metric units (grams, kilograms). The ounces listed below are ounces by weight, not fluid ounces.

1 pound = 16 ounces = 454 grams
1 kilogram = 1000 grams = 2.2 pounds

When writing these units, the following abbreviations are frequently used:

lb = pound
oz = ounce
g = gram
kg = kilogram.

Factor-Label Method

A common method of converting units is to use the “FactorLabel” method. In this method, you treat the conversion units (i.e. labels) as if they were algebraic quantities. You multiply and divide using conversion ratios (i.e. factors) crossing out units until you get the units you want.

  1. Write the quantity and its units you want to convert.
  2. Multiply it by a conversion ratio such that the units you want to get rid of are cancelled out when multiplied by this factor.
  3. Several factors can be used to get to the final units. Just remember to cancel out the units as you multiply the factors.


Following are several examples you can use to practice the Factor-Label method.

Example 1: Convert 950 grams to units of pounds.

converting one

Using a calculator, first enter 950, and then hit the division sign. Enter 454 and hit the equals sign. You should get the answer 2.09.

Example 2: Convert 64 ounces to units of kilograms.

Converting 64 oz

Using a calculator, start out the same way as in Example 1. Enter 64 and hit the division sign. Enter 16 and hit the equals sign.

You should get 4.

Now, go onto the second ratio. Leaving 4 in the display, hit the division sign. Enter 2.2 and hit the equals sign. You should get the answer 1.8.

Remember to hit the equals sign after each ratio and leave that number in the display for the next calculation!


(Originally published in Soap Guild Journal March 2008.)

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