Significant Figures Calculator
Count significant figures, round any number to N sig figs, or multiply and divide with proper sig-fig rules — with the rule explained each time.
About the Significant Figures Calculator
This significant figures calculator does three jobs: it counts the significant figures in a number exactly as written, rounds a number to any number of significant figures, and performs multiplication or division while applying the sig-fig rule automatically — the result keeps only as many significant figures as the least precise input.
The counting rules it applies are the standard ones from chemistry and physics: all non-zero digits are significant; zeros between non-zero digits are significant; leading zeros never are; and trailing zeros count only when a decimal point is present. That's why 0.004560 has four significant figures while 4,500 (written without a decimal point) has just two.
Because trailing zeros matter, enter numbers exactly as they appear in your problem — the tool reads the text you type, not just its numeric value. Everything runs instantly in your browser.
How to Use the Significant Figures Calculator
- 1Pick a mode: round to N sig figs, count sig figs, or multiply/divide with sig-fig rules.
- 2Type the number exactly as written — trailing zeros and decimal points matter.
- 3For rounding, set the number of significant figures (1–15).
- 4Read the result together with the rule explanation underneath.
Frequently Asked Questions
How many significant figures does 0.004560 have?
Four: 4, 5, 6 and the final 0. The three leading zeros only locate the decimal point and are never significant, but the trailing zero after a decimal point signals measured precision, so it counts. The calculator walks through this reasoning for any number you enter.
How do I round 3,847.29 to 3 significant figures?
Keep the first three significant digits (3, 8, 4) and look at the next digit (7) to decide the rounding: 7 rounds up, giving 3,850. Note the trailing zero here is a placeholder, not a fourth significant figure — writing 3.85 × 10³ makes that unambiguous.
What is the sig-fig rule for multiplication and division?
The result keeps as many significant figures as the factor with the fewest. Example: 2.5 (2 sig figs) × 3.42 (3 sig figs) = 8.55, which rounds to 8.6 — two significant figures. The operation mode of this calculator applies that automatically and shows the counts of both operands.
Are the zeros in 1,500 significant?
As written without a decimal point, no — 1,500 has two significant figures. Writing 1,500. (with a point) makes all four significant, and scientific notation removes all ambiguity: 1.5 × 10³ has two, 1.500 × 10³ has four.
Why do significant figures matter?
They encode how precisely a quantity was measured. Reporting a result with more sig figs than your least precise measurement claims accuracy you don't have — multiplying a 2-sig-fig measurement by anything can never honestly yield a 5-sig-fig answer.