Unit Conversion & Math Tools
Tools in This Collection
Percentage Calculator
Calculate percentages: find a percentage of a number, what percent one number is of another, or the percentage change between two values.
Ratio Calculator
Simplify a ratio of two numbers using the greatest common divisor, and see it as a decimal and percentage.
Proportion Calculator
Solve proportions by finding the missing value D in the equation A/B = C/D.
Roman Numeral Converter
Convert between Roman numerals and decimal numbers (1–3999).
Scientific Notation Converter
Convert numbers between standard decimal form and scientific notation.
Area Converter
Convert between square meters, square feet, acres, hectares, and other area units instantly.
Frequently Asked Questions
- How do I calculate a percentage of a number?
- Multiply the number by the percentage and divide by 100. For example, 15% of 200 is (200 × 15) ÷ 100 = 30. Our percentage calculator handles this and also calculates percentage change, percentage difference, and reverse percentages.
- What is a proportion and how do I solve one?
- A proportion states that two ratios are equal, like 2/3 = x/12. To solve, cross-multiply: 2 × 12 = 3 × x, so x = 8. Our proportion calculator solves for any missing value and shows the work.
- How do I convert between metric and imperial area units?
- One square meter equals about 10.764 square feet, and one acre equals about 4,047 square meters. Our area converter handles all common unit pairs including square feet, square meters, acres, hectares, and square kilometers.