Significant Figures Calculator

Count the significant figures in any number and round it to a chosen number of sig figs. Essential for scientific measurements, lab reports and any calculation where precision must be communicated honestly.

Enter a number

Decimals, integers, scientific notation, and trailing zeros are all handled.

Enter a number and press Count & round.

Rules for counting significant figures

  1. All non-zero digits are significant. 123 has 3 sig figs.
  2. Zeros between non-zero digits are significant. 1002 has 4 sig figs.
  3. Leading zeros are not significant. 0.0025 has 2 sig figs.
  4. Trailing zeros after a decimal point are significant. 2.500 has 4 sig figs.
  5. Trailing zeros in a whole number with no decimal point are ambiguous. 1500 could have 2, 3 or 4 sig figs depending on the intended precision — use scientific notation (1.5 × 10³) to make it clear.

Rounding to significant figures

To round a number to n significant figures, keep the first n significant digits and round the rest according to the usual rule (if the next digit is 5 or more, round up).

3.14159 → 3 sig figs → 3.14

1234.5 → 3 sig figs → 1230

0.006789 → 2 sig figs → 0.0068

Worked examples

Example 1 — Simple count

How many significant figures in 3.450?

Digits 3, 4, 5, 0 are all significant → 4 sig figs.

4 sig figs

Example 2 — Leading zeros

How many significant figures in 0.00048?

Leading zeros are not significant. Digits 4, 8 count → 2 sig figs.

2 sig figs

Example 3 — Rounding

Round 47.832 to 3 significant figures.

The first 3 digits are 4, 7, 8. The next digit is 3 (< 5), so no round-up.

47.8 (3 sig figs)

Example 4 — Rounding a whole number

Round 876543 to 2 significant figures.

The first 2 digits are 8, 7. The next digit is 6 (≥ 5), so round up to 88, then pad with zeros.

880,000 (2 sig figs)

Rounding Calculator

Round to decimals and place values.

Scientific Notation Converter

Convert to a × 10ⁿ form.

Decimal to Fraction Converter

Convert decimals to fractions.

Frequently asked questions

A significant figure is a digit that carries meaningful information about the precision of a measurement. Non-zero digits, zeros between non-zero digits, and trailing zeros after a decimal point are all significant.

Without a decimal point, you cannot tell whether the trailing zeros are significant. In 1500, the zeros might just be placeholders (2 sig figs) or they might indicate precise measurement (4 sig figs). Writing 1.500 × 10³ removes the ambiguity.

For multiplication and division, the answer should have the same number of sig figs as the least precise input. For addition and subtraction, the answer should have the same number of decimal places as the least precise input.