Slope Percentage Calculator
Our slope percentage calculator will help you understand what the 5% slope means and how to convert it to degrees.
The formula
grade = rise ÷ run × 100
Grade, angle and ratio
A 100% grade is 45 degrees, not vertical — the percentage is the tangent of the angle, not a fraction of a right angle. Road signs use percent, railways often use ratios like 1 in 40, and roofs are usually quoted as rise over a 12-inch run.
What a percentage is
"Per cent" means "per hundred", so a percentage is just a fraction with 100 on the bottom. 15% is 15/100, which is 0.15 as a decimal. Every percentage calculation is therefore multiplication or division by a decimal — the percent sign is bookkeeping, not a new operation.
The three questions
Almost every percentage problem is one of three:
- What is P% of N? Multiply:
N × P/100 - A is what percent of B? Divide:
A/B × 100 - A is P% of what? Divide the other way:
A ÷ (P/100)
Recognising which one you have is most of the work; the arithmetic is straightforward once you do.