# Significant Figures Calculator - Count, Round and Calculate with Sig Figs

> Free online sig fig calculator: count significant figures digit by digit, round to N sig figs or decimals with six rounding modes, and compute by sig fig rules.

- URL: https://qilingtools.com/en/math/significant-figures
- Category: Math Tools (https://qilingtools.com/en/math)
- Tags: [Math](https://qilingtools.com/en/tags/math), [Chemistry](https://qilingtools.com/en/tags/chemistry), [Physics](https://qilingtools.com/en/tags/physics), [Education](https://qilingtools.com/en/tags/education)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

Chemistry and physics lab reports, engineering work and exams all expect answers with the right number of significant figures. Enter a number — 0.004500, 1200, 1.20e3 or 6.02×10^23 all work — and the tool counts its sig figs and colors every digit by rule: non-zero digits, zeros between them and trailing zeros after a decimal point count, leading zeros are only placeholders, and trailing zeros in a whole number such as 1200 are ambiguous, so you see the possible range. Rounding mode keeps N significant figures or N decimal places using half up, half even (banker's rounding), up, down, ceiling or floor, and shows the result in plain, scientific and engineering notation with a 1–8 sig fig comparison table. Arithmetic mode combines two measurements with the textbook rules — addition and subtraction keep the least precise decimal place, multiplication and division keep the fewest significant figures — using exact decimal math, so there are no floating-point surprises like 0.1 + 0.2.

## How to use

1. Choose a mode: count, round, or sig fig arithmetic
2. Enter a number (or two measurements and an operator)
3. Read the sig fig count, the digit-by-digit explanation, the rounded value and its scientific notation

## Features

- Counts significant figures and explains every digit
- Flags ambiguous trailing zeros such as 1200
- Round to N sig figs or N decimal places
- Six rounding rules including banker's rounding
- Scientific, engineering and E notation
- Addition, subtraction, multiplication and division with sig fig rules
- Exact decimal arithmetic, no floating-point error

## FAQ

### How many significant figures does 0.00450 have?

Three. The leading 0.00 only positions the decimal point, 4 and 5 are non-zero digits, and the final 0 comes after the decimal point, meaning the measurement is precise to that place. In scientific notation it is 4.50 × 10^-3.

### How many significant figures does 1200 have?

It is ambiguous: the trailing zeros may be placeholders or measured digits. It is usually counted as 2. To show 3 or 4 sig figs, write 1.20 × 10^3 or 1.200 × 10^3, or add a decimal point: 1200.

### What is banker's rounding (round half to even)?

Digits below 5 round down and above 5 round up, but an exact 5 rounds to the nearest even digit: 2.25 → 2.2 and 2.35 → 2.4. Because ties go up half the time and down half the time, it avoids the upward bias of always rounding half up, which is why it is used in many lab and financial standards.

### What are the sig fig rules for adding versus multiplying?

For addition and subtraction, round to the least precise decimal place among the inputs: 12.11 + 18.0 = 30.1. For multiplication and division, keep as many significant figures as the input with the fewest: 2.50 × 3.1 = 7.8. In multi-step work keep an extra digit or two and round only at the end.

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