Significant Figures Calculator
Count the significant figures in any number, see exactly which digits count and why, round to a chosen precision, and get the unambiguous scientific-notation form.
Number
Type a number — trailing zeros are kept (e.g. 0.00250, 1500, 1.020).
Result
About the Significant Figures Calculator
Significant figures (sig figs) are the digits in a number that carry real, measured meaning — they tell you how precisely a quantity is known. This calculator does three things. First, it counts the significant figures in any number you type, preserving trailing zeros (which a plain calculator would silently drop) and showing a digit-by-digit breakdown so you can see exactly which figures count and which are just placeholders. Second, it rounds any value to a chosen number of significant figures using correct round-half-up rules, keeping the trailing zeros that encode the precision. Third, it converts your number to scientific notation, the form that removes all ambiguity about how many figures are significant. Sig figs matter everywhere measurements are used — in chemistry, physics, engineering and lab reports — because a result should never look more precise than the data it came from. The rules around zeros are subtle, so the visual breakdown here is built to make them obvious.
How to use this calculator
- 1 Pick a mode: "Count sig figs" to analyse a number, or "Round to sig figs" to round one.
- 2 Type your number exactly as written — keep the trailing zeros and the decimal point, because they change the count (1500 and 1500. are not the same).
- 3 Read the result: the sig-fig count with a colour-coded digit breakdown and an ambiguity note when relevant, or the rounded value in both decimal and scientific notation.
The significant-figure rules
Counting significant figures follows a fixed set of rules: 1. All non-zero digits are significant (123 has 3). 2. Zeros between non-zero digits are significant (1002 has 4; 1.02 has 3). 3. Leading zeros are never significant — they only place the decimal point (0.0012 has 2; 0.5 has 1). 4. Trailing zeros after a decimal point are significant, because writing them is a deliberate claim of precision (1.200 has 4; 0.00250 has 3; 50.0 has 3). 5. Trailing zeros in a whole number with no decimal point are ambiguous. By convention they are treated as not significant (1500 → 2, 100 → 1), but the count is uncertain. Adding a trailing decimal point removes the doubt (1500. → 4). 6. Scientific notation removes all ambiguity: every digit written in the mantissa is significant (1.20×10³ has 3, 6.022×10²³ has 4). This is why scientists prefer it. To round to N significant figures, keep the first N significant digits, round the next digit using round-half-up, and pad with trailing zeros so the result still shows exactly N figures of precision.
Frequently asked questions
How many significant figures are in 0.00500?
Three. The leading zeros (0.00) are not significant — they only place the decimal point. The 5 is significant, and the two trailing zeros come after the decimal point, so they are significant too. That gives 3 significant figures, written unambiguously as 5.00×10⁻³.
Are trailing zeros significant?
It depends on whether there is a decimal point. Trailing zeros after a decimal point are always significant (1.200 has 4, 50.0 has 3) because they show measured precision. Trailing zeros in a bare whole number are ambiguous and conventionally counted as not significant (1500 → 2, 100 → 1). Write the number with a trailing decimal point (1500.) or in scientific notation to make the count clear.
Why do scientists use significant figures?
Significant figures communicate how precisely a value is known. A measurement of 12.3 cm claims precision to a tenth of a millimetre, while 12.300 cm claims far more. Reporting too many figures makes a result look more accurate than the instrument allows; reporting too few throws away real information. Carrying sig figs through a calculation keeps the final answer honest — it should be no more precise than the least-precise measurement that went into it.
How do you round to a number of significant figures?
Keep the first N significant digits, then look at the next digit: if it is 5 or more, round the last kept digit up; otherwise leave it. Pad with trailing zeros so the answer still shows N figures. For example, 3.14159 to 3 sig figs is 3.14, 1234 to 2 sig figs is 1200 (or 1.2×10³), and 999 to 2 sig figs rounds up to 1000 (1.0×10³). This calculator does all of that and shows the result in both decimal and scientific notation.
Related tools
Keep working with numbers on UnitConv. Use the scientific notation converter to switch between standard, scientific, engineering and E-notation, the rounding and percentage calculators for everyday math, and the molar mass and other science calculators where significant figures matter in every answer.