Significant Figures Calculator — Count, Round & Apply Sig Fig Rules
Count sig figs in any number and round to a specified number of significant figures. Covers addition, subtraction, multiplication, division rules, and trailing zeros.
Significant figures communicate precision. Writing "3.5 kg" versus "3.50 kg" isn't just style — the second version says you measured to the nearest 10 grams, not 100 grams. Get the count right and round correctly with the CalcHub Significant Figures Calculator.
The Rules for Counting Sig Figs
Non-zero digits: always significant
1234 → 4 sig figsZeros between non-zero digits: always significant
1004 → 4 sig figs 3.07 → 3 sig figsLeading zeros: never significant
0.0034 → 2 sig figs (the zeros are just placeholders)Trailing zeros:
- After a decimal point: always significant
- Without a decimal point: ambiguous
The decimal point indicator
Adding a decimal point to a trailing zero makes it significant:- → 4 sig figs
Quick Reference Table
| Number | Sig Figs | Reason |
|---|---|---|
| 42 | 2 | Both non-zero |
| 3.14 | 3 | All non-zero |
| 0.005 | 1 | Leading zeros don't count |
| 0.0500 | 3 | Trailing zeros after decimal |
| 1300 | 2 or 3 or 4 | Ambiguous — clarify with sci notation |
| 1.300 × 10³ | 4 | Scientific notation makes it clear |
| 10,000 | 1 (probably) | Need context or sci notation |
Rounding to n Significant Figures
Find the nth sig fig, look at the next digit, and round normally.
Round 0.004682 to 2 sig figs: The sig figs are 4, 6, 8, 2. The 2nd sig fig is 6. The next digit is 8 (≥ 5), so round up. Result: 0.0047 Round 84,500 to 3 sig figs: Sig figs: 8, 4, 5. Next digit is 0 (< 5), keep as-is. Result: 84,500 (but write as 8.45 × 10⁴ to be unambiguous)Operations and Sig Figs
Addition and Subtraction: Match Decimal Places
Your answer can't be more precise than the least precise measurement's decimal position.
Example: 12.52 (2 decimal places)
+ 0.8 (1 decimal place)
+ 1.346 (3 decimal places)
= 14.666 → round to 1 decimal place → 14.7Multiplication and Division: Match Sig Fig Count
Your answer gets the same number of sig figs as the factor with the fewest.
Example: 4.52 × 3.1 = 14.012 → 14 (2 sig figs, matching 3.1) Example: 84.0 / 3.0 = 28.0 → 28 (2 sig figs)Exact Numbers and Counting Numbers
Not everything has sig figs. Counted quantities (12 eggs, 5 people) are exact — they don't limit your answer's precision. Mathematical constants like π can be used to any precision you need. Defined values (1 inch = 2.54 cm exactly) are also exact.
Why doesn't 1500 have 4 sig figs automatically?
Because the trailing zeros in a whole number without a decimal point might just be placeholders — the measurement might only be precise to the hundreds or thousands place. This ambiguity is why scientific notation exists. Write 1.500 × 10³ for 4 sig figs, 1.5 × 10³ for 2.
When do sig fig rules matter in practice?
They matter most in lab reports, engineering calculations, and any quantitative science where you're combining measurements. In pure mathematics (no measurement involved), there's no concept of sig figs. In everyday cooking or casual estimation, they're usually ignored — nobody measures 2.5 cups of flour to 2 sig figs.
What's the difference between significant figures and decimal places?
Decimal places count digits after the decimal point regardless of significance. Significant figures count all meaningful digits in a number. For 0.0030: it has 4 decimal places but only 2 significant figures.