🔬 Significant Figures Calculator
Round numbers to sig figs or count how many a number has — with step-by-step explanation
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The 5 Rules of Significant Figures

  • 1
    All non-zero digits are significant. In 284, all three digits (2, 8, 4) are significant → 3 sig figs.
  • 2
    Zeros between non-zero digits are significant. In 3007, the two zeros between 3 and 7 are significant → 4 sig figs.
  • 3
    Leading zeros are NOT significant. In 0.0042, the three leading zeros are not significant. Only 4 and 2 are → 2 sig figs.
  • 4
    Trailing zeros after a decimal point ARE significant. 1.500 has 4 sig figs; the two trailing zeros indicate precision to the thousandths place.
  • 5
    Trailing zeros in a whole number are ambiguous. 1200 could have 2, 3, or 4 sig figs. Use scientific notation (1.2 × 10³ = 2 sig figs) to be unambiguous.

Rounding Examples

OriginalRoundedSig Figs
0.0034070.003413
12345123003
0.105000.1053
9876.5498803
0.0005980.0006003
1,234,5671,230,0003

Why Do Significant Figures Matter?

Significant figures communicate the precision of a measurement. If a scale reads 12.3 g, you know the mass to the nearest tenth of a gram — writing 12.300 g would falsely imply precision to the nearest milligram. In science and engineering, misrepresenting precision can lead to errors in calculations, reports, and real-world applications.

When multiplying or dividing measurements, your answer should have the same number of sig figs as the measurement with the fewest sig figs. When adding or subtracting, round to the same number of decimal places as the least precise measurement.

Sig Figs in Scientific Notation

Scientific notation removes all ambiguity. The coefficient always shows exactly how many digits are significant:

1.20 × 10⁴ → 3 sig figs (the trailing zero after the decimal is significant).

1.2 × 10⁴ → 2 sig figs.

If you need to express 12000 with exactly 3 sig figs, write it as 1.20 × 10⁴.

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Quick Sig Fig Count

0.0052 → 2 sig figs (leading zeros don't count)

1003 → 4 sig figs (zeros between non-zeros count)

2.500 → 4 sig figs (trailing zeros after decimal count)

1500 → 2–4 sig figs (ambiguous — use scientific notation)

Math Operations

× or ÷: Answer has the same sig figs as the least precise input.

+ or −: Answer is rounded to the same decimal place as the least precise input.

Example: 12.3 × 1.456 = 17.9 (3 sig figs, limited by 12.3)

🔭 Related Tool

Working with very large or very small numbers? Convert to scientific notation first.

Scientific Notation Converter →

Frequently Asked Questions

What are significant figures?

Significant figures (also called significant digits or sig figs) are the digits in a number that carry meaningful information about its precision. They communicate how precisely a measurement was made — whether with a ruler, a scale, or a laboratory instrument. The more significant figures a number has, the more precise the measurement it represents.

What are the rules for counting significant figures?

There are five core rules: (1) All non-zero digits are significant — 123 has 3 sig figs. (2) Zeros between non-zero digits are significant — 1003 has 4 sig figs. (3) Leading zeros are never significant — 0.0045 has 2 sig figs. (4) Trailing zeros after a decimal point are significant — 1.500 has 4 sig figs. (5) Trailing zeros in a whole number are ambiguous — 1500 might have 2, 3, or 4 sig figs. Use scientific notation to remove the ambiguity.

How do you round a number to significant figures?

Identify the last significant digit you want to keep, then look at the next digit. If it is 5 or greater, round up the last kept digit by 1. If it is less than 5, leave it unchanged. For example, rounding 0.003407 to 3 sig figs gives 0.00341. Rounding 5,482 to 2 sig figs gives 5,500.

Why do significant figures matter?

Significant figures prevent you from reporting a false level of precision. If you measure something with a ruler accurate to 1mm and report the result to 6 decimal places, the extra digits are meaningless noise. When multiplying or dividing, the result should have the same number of sig figs as the least precise input. When adding or subtracting, the result should match the fewest decimal places of any input.

How do significant figures work in scientific notation?

Scientific notation removes all ambiguity about significant figures. The coefficient always shows exactly how many digits are significant. For example, 1.20 × 10⁴ has 3 sig figs, while 1.2 × 10⁴ has 2 sig figs. Writing 12,000 in scientific notation as 1.200 × 10⁴ makes it clear that all four digits are significant. Use our Scientific Notation Converter to convert numbers before rounding.

How many sig figs should I use in my answer?

It depends on the operation. For multiplication and division, use the same number of sig figs as the measurement with the fewest. For addition and subtraction, keep digits only as far right as the least precise measurement allows. In most chemistry and physics lab work, 3 sig figs is the standard unless your instrument justifies more.