Probability Calculator vs Standard Deviation Calculator

Basic probability = Favorable Outcomes / Total Outcomes. Rolling a 3 on a die: 1 favorable outcome / 6 total outcomes = 1/6 or about 16.7%.

Probability is favorable outcomes divided by total outcomes. Odds are favorable outcomes to unfavorable outcomes. A probability of 1/6 equals odds of 1:5 (1 for to 5 against).

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.