Quick Conversion Tricks

When the denominator divides cleanly into 100, you can convert in one step.

• 3/5: multiply top and bottom by 20 to get 60/100 = 60%
• 7/25: multiply by 4 to get 28/100 = 28%
• 9/20: multiply by 5 to get 45/100 = 45%

If the denominator does not fit neatly into 100, fall back on the rule: divide the numerator by the denominator, then multiply by 100.

Anchors To Memorize

Keep a handful of fractions in your back pocket, and you can build the rest:

• 1/2 = 50%
• 1/4 = 25%
• 1/5 = 20%
• 1/8 = 12.5%
• 1/3 ≈ 33.3%

From these you derive almost anything in your head. Three-eighths? That is 3 × 12.5% = 37.5%. Build from what you already know instead of dividing from scratch.