Carpentry & Building Construction © 2004

Math Activities :

Self-Check Math Activity 7

Converting Decimals to Fractions

Using measurements may involve decimals. Decimals are based on the number 10. Any number to the right of the decimal point is less than a whole number. For example, 0.1 means one-tenth, 0.01 is one-hundredth, and 0.001 is one-thousandth.

Sometimes a decimal needs to be changed into a fraction that has a numerator and denominator. It is easy to convert 0.01 into a fraction. You just write 1/100. However, converting fractions in which the denominator is a number other than 10 can be more challenging. To save time, carpenters may use a calculator to convert from one form to the other, or they may use a conversion table.

Terms, Symbols, & Abbreviations
decimals - numbers expressed as powers of 10
fraction - a portion of a whole, expressed as numerator/denominator

Practice Exercises

Show 6.125 as a mixed number with a fraction.
Step 1	Separate the number 6 to the left of the decimal point. Numbers to the left of the
	decimal point are whole numbers and do not need to be converted.
Step 2	Write the number to the right of the decimal point as a fraction.
	.125 = 125/1000
Step 3	Write the result as a mixed number.
	6.125 = 6 125/1000
Step 4	Reduce the fraction to lowest terms. Both 125 and 1000 are divisible by 125.
	6 125/1000 = 6 1/8

Decimal-Fraction Equivalents table (19.0K)

In the Decimal/Fraction Equivalents table provided here, the numbers are arranged in columns. The lowest numbers are in the first two columns. The highest numbers are in the last pair of columns. The decimal equivalents are to the right of the fractions. For example, 1/64 is equal to 0.015625.

Using this table, convert 0.6875 to a fraction.

Step 1	Find 0.6875 on the table.
Step 2	The fraction to the left is 11/16. This is the equivalent of 0.6875.

Problem Exercises


1.	An installation requires a 0.375'' drill bit, which is the same as
		A)	1/8
		B)	1/4
		C)	3/8
		D)	5/8


2.	The thickness of a flooring material is 0.1875'', or
		A)	1/16''
		B)	1/8''
		C)	1/4''
		D)	3/16''


3.	The plywood ordered for a job is 0.625'', or
		A)	3/8"
		B)	5/8"
		C)	3/16"
		D)	5/16"


4.	The recommended gap for assembling a fixture is 0.875'', or
		A)	5/8''
		B)	3/4''
		C)	7/8''
		D)	7/16''


5.	A carpenter needs to drill a 0.0625'' pilot hole, which is the same as
		A)	1/16''
		B)	1/32 #039;'
		C)	1/8''
		D)	1/4''