Significant Figures Calculator
Count significant figures in any number, or round a number to a specific number of significant figures. Shows scientific notation.
5 rules: (1) Non-zero digits are sig. (2) Sandwiched zeros are sig (1001→4). (3) Leading zeros never sig (0.042→2). (4) Trailing zeros with decimal are sig (3.20→3). (5) Trailing zeros without decimal are ambiguous.
Sig fig rules (IB/AP/A-Level):
- Non-zero digits are always significant
- Zeros between sig figs are significant (e.g. 1001 → 4)
- Leading zeros are never significant (e.g. 0.0042 → 2)
- Trailing zeros with decimal point are significant (e.g. 3.20 → 3)
- Trailing zeros without decimal are ambiguous (use scientific notation)
Significant Figures by Curriculum
| Curriculum / Exam | Sig figs emphasis | Typical requirement |
|---|---|---|
| 🇺🇸 AP Chemistry / AP Physics | High — penalised for wrong sig figs | 3 sig figs in most calculations |
| 🇺🇸 US SAT / ACT | Low — rarely tested explicitly | Round to given decimal places |
| 🇬🇧 UK A-Level Physics/Chem | High — mandatory in lab work | 3 sig figs unless data specifies |
| 🇬🇧 UK GCSE | Medium — tested in maths | 1, 2, or 3 sig figs depending on question |
| 🌍 IB Physics/Chemistry | Very high — strict marking | Match lowest sig figs in data |
| 🇩🇪 Germany (Gymnasium) | Medium — used in Physik/Chemie | Signifikante Stellen — 3 common |
| 🇯🇵 Japan (高校) | Medium — 有効数字 | 2–3 significant figures typical |
| 🌍 Engineering worldwide | Context-dependent | 3–6 sig figs typical |
Frequently Asked Questions
How many significant figures does 0.00420 have?
0.00420 has 3 significant figures: 4, 2, and 0 (the trailing zero after 2 is significant because there is a decimal point). The leading zeros (0.00) are NOT significant — they only show the magnitude.
Is 1200 2, 3, or 4 significant figures?
Ambiguous! Without a decimal point, trailing zeros may or may not be significant. To remove ambiguity, use scientific notation: 1.2 × 10³ (2 sig figs), 1.20 × 10³ (3 sig figs), 1.200 × 10³ (4 sig figs). A decimal point after 1200. (1200.) implies 4 sig figs.
How do sig figs work in multiplication and division?
Answer should have the same number of sig figs as the measurement with the fewest. Example: 3.2 × 4.567 = 14.6144 → round to 2 sig figs → 15. (3.2 has 2 sig figs).
How do sig figs work in addition and subtraction?
Answer should have the same number of decimal places as the measurement with the fewest. Example: 12.52 + 349.0 + 8.24 = 369.76 → round to 1 decimal place → 369.8 (because 349.0 has 1 decimal place).