mode
Significant Figures Counter
Count the number of significant figures in any number instantly. Supports integers, decimals, trailing zeros, and scientific notation.
Click to show tips
Try an Example
Pick a scenario to see how the calculator works, then adjust the values
Count Sig Figs
Count the significant figures in a measurement with trailing zeros
Key values: 0.00340 · count mode · 3 sig figs
Round to Sig Figs
Round a scientific measurement to 3 significant figures
Key values: 123456 · round to 3 · = 123000
Multiply with Sig Figs
Apply sig fig rules when multiplying two measured values
Key values: 12.5 x 3.2 · multiply · limiting factor
Rules for Counting Significant Figures
- All non-zero digits are significant. has 4 sig figs.
- Zeros between non-zero digits are significant. has 4 sig figs.
- Leading zeros are never significant. has 2 sig figs (the 4 and 2).
- Trailing zeros after a decimal point are significant. has 4 sig figs.
- Trailing zeros in a whole number are ambiguous. could be 2, 3, or 4 sig figs depending on context. Use scientific notation to clarify.
Examples
| Number | Sig figs | Reasoning |
|---|---|---|
| 0.0035 | 2 | Leading zeros don't count |
| 100.0 | 4 | Trailing zero after decimal counts |
| 5,020 | 3 | Trailing zero without decimal: ambiguous, assumed 3 |
| 0.00800 | 3 | Leading zeros don't count; trailing zeros after decimal do |
| 1.00 × 10³ | 3 | Scientific notation removes ambiguity |
| 6.022 × 10²³ | 4 | Avogadro's number to 4 sig figs |
Exact Numbers
Some numbers have infinite significant figures because they are defined, not measured:
- Counting: “12 eggs” — exactly 12, not 11.5 or 12.4
- Defined conversions: 1 inch = 2.54 cm (exactly, by definition)
- Mathematical constants used as exact values in formulas
Exact numbers never limit the sig figs of a calculation result.
Scientific Notation Removes Ambiguity
Is 4,500 precise to 2, 3, or 4 sig figs? The notation doesn't tell you. Scientific notation solves this:
- — 2 sig figs
- — 3 sig figs
- — 4 sig figs
Frequently Asked Questions
How do I count significant figures?
All non-zero digits are significant. Zeros between non-zero digits are significant. Leading zeros are never significant. Trailing zeros after a decimal point are significant. Trailing zeros in a whole number without a decimal point are ambiguous.
How many significant figures does 0.00450 have?
It has 3 significant figures: the 4, 5, and trailing 0. The leading zeros (0.00) are not significant because they only indicate the position of the decimal point. The trailing zero after the 5 is significant because it follows a decimal point.
Are trailing zeros significant in whole numbers?
Trailing zeros in a whole number like are ambiguous. It could have 2, 3, or 4 significant figures depending on context. Use scientific notation to clarify: is 2 sig figs, is 3 sig figs, and is 4 sig figs.
What are exact numbers in significant figures?
Exact numbers have infinite significant figures because they are defined, not measured. Examples include counting (12 eggs is exactly 12), defined conversions (1 inch = exactly 2.54 cm), and mathematical constants used as exact values. Exact numbers never limit the sig figs of a result.
Why does scientific notation help with significant figures?
Scientific notation removes ambiguity about trailing zeros. For example, 4500 could be 2, 3, or 4 sig figs, but is clearly 3 sig figs. Only the digits in the coefficient count as significant.
Related mode Variants
Explore more mode options