Sig Fig Calculator

Count significant figures with every digit colour-coded by the rule that applies, round any number to a chosen number of sig figs, and do calculations that follow the sig-fig rules for multiplication and addition.

Count significant figures

  • significant
  • placeholder zero (not significant)
Significant figures
4
Decimal places
6
Scientific notation
4.050 × 10⁻³
  • 0 — Leading zero: only a placeholder
  • 0 — Leading zero: only a placeholder
  • 0 — Leading zero: only a placeholder
  • 4 — Non-zero digit: always significant
  • 0 — Captive zero between significant digits: significant
  • 5 — Non-zero digit: always significant
  • 0 — Trailing zero after a decimal point: significant

Round to significant figures

Rounded
0.0041
In scientific notation
4.1 × 10⁻³

Calculate with sig-fig rules

Answer (correct sig figs)
39
Unrounded
38.812
Scientific
3.9 × 10¹

Multiplication/division: keep the fewest significant figures of any input. 12.52 has 4, 3.1 has 2 → answer gets 2.

Ask the tutor about your result

An AI tutor reads your inputs and results above and explains them in plain English. The numbers come from the calculator; the explanation is AI-written, so check it against your notes.

The five sig-fig rules, one at a time

Step through the five rules. Yellow digits are significant; struck-out zeros are placeholders; hatched zeros are ambiguous.

4,508 → 4 significant figures

Non-zero digits always count, and a zero trapped between them (a captive zero) counts too.

The significant figure rules

  1. Non-zero digits are always significant.
  2. Captive zeros between non-zero digits are significant: 4,508 has 4.
  3. Leading zeros are never significant: 0.0072 has 2.
  4. Trailing zeros after a decimal point are significant: 0.00720 has 3, and 2.0 has 2.
  5. Trailing zeros in a whole number without a decimal point are ambiguous: 1200 could have 2, 3 or 4. Most courses count 2. Write 1.20 × 10³ or “1200.” to be clear.

Exact numbers (counted items, defined conversions like 100 cm = 1 m) have unlimited significant figures and never limit a result.

Rules for calculations

Multiplying or dividing: the answer keeps as many sig figs as the input with the fewest. 12.52 × 3.1 = 38.812 → 39 (2 sig figs, because of 3.1).

Adding or subtracting: the answer is rounded to the least precise decimal place. 12.52 + 3.1 = 15.62 → 15.6 (tenths, because of 3.1).

In multi-step problems, keep extra digits along the way and round once at the end, otherwise rounding errors accumulate.

Frequently asked questions

Is 0.01 one or two significant figures?

One. The zeros before the 1 are leading zeros that only locate the decimal point. 0.010 would have two, because the trailing zero after the decimal point was measured.

How many sig figs does 1000000 have?

One by the usual convention, since trailing zeros without a decimal point are ambiguous. To show more, write it in scientific notation: 1.000 × 10⁶ has 4.

How do you determine sig figs in a calculation?

For × and ÷, keep the fewest significant figures of any input. For + and −, round to the least precise decimal place. For log, give as many decimal places as the input has sig figs; for powers, keep the base’s sig figs. Exact numbers (counts, defined conversions) never limit the answer. Round once, at the end.

Can you do sig figs on a calculator?

A normal calculator shows every digit, so you apply the rules yourself; a TI-84 can fix the decimal places (MODE → Float) but not significant figures. This calculator applies the rules for you and explains which one it used.

How many sig figs does 100 have?

By the usual textbook convention, 1: the trailing zeros are ambiguous placeholders. 100. (with a decimal point) has 3, and 1.00 × 10² has 3.

Do zeros after a decimal count?

Trailing zeros after the decimal point do (2.50 has 3). Leading zeros before the first non-zero digit don’t (0.05 has 1).

How do I round 0.004050 to 2 sig figs?

The first two significant digits are 4 and 0; the next digit is 5, so round up: 0.0041.