Percentage Calculator vs Standard Deviation Calculator

Multiply the number by the percentage divided by 100. For example, 30% of 250 = 250 × 0.30 = 75. This is the most common percentage calculation used in discounts, tips, taxes, and commissions.

Subtract the old value from the new value, divide by the old value, then multiply by 100. Formula: ((New - Old) / Old) × 100. A positive result is an increase; negative is a decrease. For example, going from 80 to 100 is a 25% increase.

Standard deviation measures the spread or variability in a dataset — how far individual values typically stray from the mean. A small standard deviation means values cluster tightly around the average. A large one means they're spread out widely. It's the most widely used measure of statistical dispersion.

Use population standard deviation (σ, divides by N) when you have data for the entire group you're studying. Use sample standard deviation (s, divides by N-1) when your data is a sample drawn from a larger population — the N-1 correction (Bessel's correction) produces an unbiased estimate. In practice, you almost always use sample standard deviation.