How to Convert a Decimal to a Ratio

How Do I Change a Decimal to a Ratio?

To convert a decimal to a ratio, first write the decimal as a fraction, then simplify it, and finally write the fraction as a ratio. For 0.004, write it as 4 over 1000, simplify to 1 over 250, and read it as the ratio 1:250. This tells you there is one of the first quantity for every 250 of the second.

Step by Step: Change 0.004 to a Ratio

Start with 0.004. Count the decimal places: there are three, so the denominator is 1000, giving the fraction 4/1000. Divide the numerator and denominator by their greatest common divisor, 4, to get 1/250. Write the fraction as a ratio by putting the numerator first and the denominator second: 1:250.

Converting Decimals That Are Not Less Than One

Decimals greater than one convert the same way. The decimal 1.25 equals the fraction 125/100, which simplifies to 5/4, so it becomes the ratio 5:4. The decimal 0.5 equals 5/10, which simplifies to 1/2, so it becomes the ratio 1:2. The process never changes: decimal to fraction, simplify, then ratio.

When to Use a Decimal vs a Ratio

Use a decimal when you want the value as a single number, and use a ratio when you want to compare two quantities side by side. A 0.004 concentration means 0.4%, while the ratio 1:250 means one part per 250 parts. Both say the same thing, but a ratio is often clearer when mixing or measuring.