0.4 as a fraction is 2/5. As a percent it is 40%. The fraction is in lowest terms: the numerator and denominator share no common factor other than 1.
How to convert 0.4 to a fraction
Step 1. Write 0.4 over a power of ten. It has 1 digit after the decimal point, so the denominator is 10: 0.4 = 4/10.
Step 2. Find the greatest common divisor of 4 and 10, which is 2.
Step 3. Divide the top and bottom by 2: 4 ÷ 2 = 2 and 10 ÷ 2 = 5. The result is 2/5.
The denominator 5 factors into 5, so this decimal terminates, as every decimal that is written with a finite number of digits does.
0.4 compared with nearby decimals
These decimals have the same number of places as 0.4, so the same method gives their fractions:
| Decimal | Fraction | Percent |
|---|---|---|
| 0.2 | 1/5 | 20% |
| 0.3 | 3/10 | 30% |
| 0.5 | 1/2 | 50% |
| 0.6 | 3/5 | 60% |
Multiples of 0.4
Scaling the fraction is a quick way to check your work. Each row multiplies 0.4 (2/5) by a whole number:
| Multiple | Decimal | Fraction | Mixed number |
|---|---|---|---|
| 2 × 0.4 | 0.8 | 4/5 | 4/5 |
| 3 × 0.4 | 1.2 | 6/5 | 1 1/5 |
| 4 × 0.4 | 1.6 | 8/5 | 1 3/5 |
| 5 × 0.4 | 2 | 2 | 2 |
| 10 × 0.4 | 4 | 4 | 4 |
When to keep the fraction
A fraction with denominator 5 is not a standard ruler fraction, so for measuring you may need the nearest 1/16 or 1/32 instead. Use the calculator above and choose a precision to round 0.4 to the closest ruler fraction.
Change the decimal in the calculator above to convert any other number; leave the precision on Exact fraction for the precise answer.