Significant Figures Calculator

Significant figures calculator: count, round and calculate

This significant figures calculator does the three jobs a chemistry or physics problem needs. Count shows every digit of a number colour-coded — significant, leading zero or ambiguous trailing zero — with the rule that applies to each. Round gives a number to any count of significant figures, in ordinary and scientific notation. Calculate works out a sum, product or a mixed calculation with brackets and applies the sig-fig rule at every step, keeping the intermediate results unrounded until the final answer.

It reads decimals, whole numbers and scientific notation (6.02e23, 1.20 × 10^3, 6.022×10²³) and works on the exact digits you type, with whole-number arithmetic instead of binary floating point, so 2.45 rounds the way the rule says rather than the way a computer happens to store it.

How to use the Significant Figures Calculator

1. Choose Count, Round or Calculate.
2. Type the number — or, for Calculate, the whole expression with + − × ÷ and brackets.
3. For rounding, set the number of significant figures; choose how an exact 5 is rounded if your course uses round-to-even.
4. Read the answer, its scientific notation and the explanation: digit colours, the rounding place, or the step-by-step table.
5. Copy the result into your lab report or homework.

Significant Figures Calculator features

Significant figures rules

1. Non-zero digits are always significant: 4.56 has 3.
2. Zeros between non-zero digits (captive zeros) are significant: 1005 has 4.
3. Leading zeros are never significant — they only place the decimal point: 0.0045 has 2.
4. Trailing zeros after a decimal point are significant: 4.500 has 4, and so has 100.0.
5. Trailing zeros in a whole number without a decimal point are ambiguous: 1200 may have 2, 3 or 4. Write 1.20 × 10³ (3) or “1200.” (4) to be clear; this calculator counts the minimum, 2.
6. Scientific notation: count only the digits of the number in front of × 10ⁿ — 6.022 × 10²³ has 4. The power of ten is never counted.

Sig figs in calculations

Multiplying and dividing: the answer has as many significant figures as the measurement with the fewest. 3.14159 × 2.1 = 6.597… → 6.6 (2 s.f., because 2.1 has 2).

Adding and subtracting: the answer is rounded to the last decimal place that every number has — count decimal places, not significant figures. 12.11 + 18.0 + 1.013 = 31.123 → 31.1, because 18.0 is only known to the tenths.

Mixed calculations: work in the usual order, note how many figures each intermediate result is entitled to, but carry the unrounded values forward. (12.11 + 18.0 + 1.013) × 2.0: the sum 31.123 is good to 3 s.f.; × 2.0 (2 s.f.) gives 62.246 → 62. Rounding the sum first would give the same here, but in longer chains early rounding drifts.

Exact numbers — counts such as 3 trials and defined conversions such as 100 cm in 1 m — have unlimited significant figures and never limit the answer. Leave them out of the rule, or type them with extra zeros (3.0000).

Rounding to significant figures

Find the last digit to keep and look at the next one: 5 or more rounds up, less than 5 leaves it. 0.0004567 to 2 s.f. is 0.00046; 123,456 to 2 s.f. is 120,000 — better written 1.2 × 10⁵. OpenStax Chemistry 2e (section 1.5, checked 24 October 2026) and many lab courses round an exact 5 with nothing after it to the even digit (92.85 → 92.8) to avoid bias; choose that option if yours does. For decimal places, banker’s rounding or the nearest multiple, use the rounding calculator, and to switch between notations try the scientific notation converter.