Practice significant-figure rules with step-by-step feedback — built for high-school and intro-college chemistry/physics students (AP Chemistry, IB Physics, A-level).
It's a sandbox, not just a calculator: type a number and your own sig-fig count, and the tool tells you whether you were right and why, walking through the standard rules.
The 5 rules it teaches
- Non-zero digits are always significant.
- Zeros between non-zero digits are significant (captive).
- Leading zeros are never significant.
- Trailing zeros ARE significant when a decimal point is present.
- Trailing zeros are AMBIGUOUS without a decimal — conservative convention treats them as not significant; scientific notation resolves the ambiguity.
Three modes
- Practice — enter a number, guess its sig-fig count, get feedback + the digit-by-digit breakdown (green = significant, grey strikethrough = leading, yellow = trailing-with-decimal, red = ambiguous trailing).
- Round — round a number to N sig figs and to scientific notation, preserving trailing zeros so the sig-fig count is honest.
- Propagate — given two measured values and an operation (+/−/×/÷), apply the propagation rule: fewest decimal places for +/−, fewest sig figs for ×/÷.
Accepts integers, decimals, leading zeros, and scientific notation (1.23e4, 1.23E4, 1.23×10^4).