Our Significant Figures Calculator rounds any number to your chosen number of significant figures instantly. Perfect for chemistry, physics, and engineering calculations where precision matters.
Significant Figures Calculator
What Are Significant Figures?
Significant figures (sig figs) are the meaningful digits in a measurement that carry actual precision. They tell you how precisely a value was measured or calculated. The rules are used in chemistry, physics, biology, and engineering to avoid overstating precision.
Rules for Counting Significant Figures
- All non-zero digits are significant. (1234 → 4 sig figs)
- Zeros between non-zero digits are significant. (1004 → 4 sig figs)
- Leading zeros are NOT significant. (0.0045 → 2 sig figs)
- Trailing zeros after a decimal ARE significant. (3.500 → 4 sig figs)
- Trailing zeros without a decimal are ambiguous. (1200 → 2, 3, or 4 sig figs depending on context)
Sig Fig Examples
| Number | Sig Figs | Reason |
|---|---|---|
| 4500 | 2 | Trailing zeros, no decimal |
| 4500. | 4 | Decimal point makes zeros significant |
| 0.00340 | 3 | Leading zeros not significant; trailing zero after decimal is |
| 6.022 × 10²³ | 4 | Scientific notation — all digits significant |
FAQs
How many sig figs should I use?
Use the same number of significant figures as the least precise measurement in your calculation. For example, if your least precise measurement has 3 sig figs, round your answer to 3 sig figs.
Are exact numbers significant?
Exact numbers (like counted quantities or defined constants) have infinite significant figures and do not limit your answer’s precision.
Are leading zeros significant figures?
No. Leading zeros (zeros before the first non-zero digit) are never significant. For example, 0.0045 has only 2 significant figures.
Are trailing zeros after a decimal point significant?
Yes. Trailing zeros that appear after a decimal point are always significant. For example, 3.500 has 4 significant figures.