Significant Figures Calculator
Round any number to a given number of significant figures. Essential for scientific calculations, lab reports, and engineering work where precision matters.
Advertisement
Calculator
See your Significant Figures Calculator results
Enter your email to unlock results — free forever.
No spam, ever. Unsubscribe at any time.
Advertisement
Formula
Round to n significant figures: preserve n meaningful digits
Significant figures count from the first non-zero digit. To round to n sig figs: find the nth significant digit, round based on the (n+1)th digit, and replace remaining digits with zeros if before the decimal point. Trailing zeros after a decimal point are significant.
How to use the Significant Figures Calculator
- 1
Enter your number
- 2
Enter your significant figures
- 3
Read your results instantly
Results update in real time as you type.
Advertisement
The rules for counting significant figures
Rule 1: All non-zero digits are significant (1–9 always count). Rule 2: Zeros between non-zero digits are significant (1001 has 4 sig figs). Rule 3: Leading zeros are NOT significant (0.0023 has 2 sig figs). Rule 4: Trailing zeros after a decimal point ARE significant (2.50 has 3 sig figs). Rule 5: Trailing zeros before a decimal point are ambiguous — use scientific notation to clarify (1.20×10³ has 3 sig figs).
Why significant figures matter in science
Significant figures communicate measurement precision. A ruler marked in millimeters can measure to ±0.5mm, yielding 3–4 sig figs for typical lengths. A high-precision laser interferometer might yield 9–12 sig figs. Reporting more digits than your measurement precision supports is misleading — it implies false accuracy.
In multi-step calculations, errors compound. The rule: your result can't be more precise than your least-precise input. Addition/subtraction: keep the same number of decimal places as the least precise input. Multiplication/division: keep the same number of significant figures as the input with the fewest.
Advertisement
Scientific notation and sig figs
Scientific notation makes significant figures unambiguous. 1200 might have 2, 3, or 4 sig figs — it's unclear. But 1.2×10³ has exactly 2, 1.20×10³ has 3, and 1.200×10³ has 4.
In chemistry and physics labs, all reported measurements should use scientific notation with the appropriate number of significant figures. This isn't pedantry — it prevents real errors in calculations where precision matters, like medication dosing or structural engineering.
Tips & Insights
When in doubt, use scientific notation
To eliminate ambiguity about trailing zeros, express your answer in scientific notation. It's always clear: 3.00×10⁴ has three sig figs, no ambiguity.
Exact numbers have infinite sig figs
Counting numbers (like '3 people') and defined conversions (like '1 inch = 2.54 cm exactly') have infinite significant figures and don't limit the precision of your result.
Worked Examples
Chemistry lab measurement
0.00456 — three significant figures (4, 5, 6). Leading zeros are not significant. The result is rounded to the nearest hundred-thousandth.
Large number
3,850,000 (or 3.85×10⁶). Rounded to 3 sig figs, the trailing zeros are placeholders, not significant.
Advertisement
Frequently Asked Questions
What are significant figures?
Significant figures are the meaningful digits in a number that contribute to its precision. Leading zeros don't count, but trailing zeros after a decimal point do.
How many significant figures should I use?
Match the number of significant figures in your least precise measurement. In multi-step calculations, carry one extra sig fig through intermediate steps, then round the final answer.
Are zeros significant?
It depends on position: zeros between non-zero digits are significant (1001 = 4 sig figs). Leading zeros are not significant (0.0023 = 2 sig figs). Trailing zeros after a decimal are significant (3.50 = 3 sig figs).
Advertisement