Significant Figures Calculator – Sig Figs

Significant figures capture real measurement precision. The number 0.00340 carries three sig figs — the leading zeros merely locate the decimal, while the trailing 0 after the 4 is measured and meaningful. Sandwiched zeros always count (1005 has four), and trailing zeros in a whole number like 1500 are ambiguous (2–4 sig figs) unless written 1.500×10³. Arithmetic follows two rules: multiplication keeps the fewest sig figs of its inputs (4.56×1.4 = 6.4, two sig figs), while addition keeps the fewest decimal places (2.5 + 3.42 = 5.9, one decimal). The calculator counts sig figs for any input, rounds results to your chosen precision, and annotates which rule fired. Scientific notation display removes ambiguity entirely: 45,600 written 4.56×10⁴ is unambiguously three sig figs.

1. 1

   Enter a number

   Any format — decimal, whole, scientific notation

2. 2

   Count the significant digits

   Leading zeros drop out; captive and measured trailing zeros stay

3. 3

   Round to target sig figs

   Choose how many figures to keep; the tool rounds correctly

4. 4

   Apply arithmetic rules

   Products keep fewest sig figs; sums keep fewest decimals

• 1

  0.00340 → 3 sig figs; 1005 → 4; 1.500×10³ → 4

• 2

  Multiplying: answer keeps the fewest sig figs among inputs

• 3

  Adding: answer keeps the fewest decimal places among inputs

• Counting leading zeros as significant in 0.00340

• Reading 1500 as exactly two sig figs — it is ambiguous without notation

• Keeping full calculator digits after multiplying 4.56×1.4 (6.384 → 6.4)

• Applying the sig-fig rule to additions, where decimal places govern