Significant Figures Calculator
Count the sig figs in any number digit by digit, round to the number of sig figs you need, and do the math with the right rounding rule shown step by step.
Sig figs cost points on almost every chemistry and physics assignment, and the rules change depending on whether you are multiplying or adding. Type a number to see which digits count and why, or type the whole calculation and get the answer rounded the way your teacher expects — with the rule that decided it.
Try:
How many significant figures? Trailing zeros with no decimal point count as not significant, the rule most classes use.
0 / 0 correct
The sig-fig rules, in one place
- Non-zero digits always count. 2.54 has 3.
- Zeros between non-zero digits count. 4005 has 4.
- Leading zeros never count. They only place the decimal: 0.0045 has 2.
- Trailing zeros count only with a decimal point. 12.300 has 5 and 1200. has 4, but 1200 is ambiguous — most classes count it as 2. Scientific notation removes the doubt: 1.20 × 103 has 3.
- Multiplying or dividing: the answer keeps as many sig figs as the number with the fewest.
- Adding or subtracting: the answer is rounded to the least precise decimal place, not the fewest sig figs. 12.11 + 18.0 = 30.1.
- Don’t round in the middle. In a multi-step problem, keep the extra digits and round once at the end. The Calculate tab does exactly this and shows the precision of each step.
- Exact numbers don’t limit you. Counts (3 trials) and defined values (100 cm in 1 m) have unlimited sig figs. Put them in square brackets, like
2.50 × [3]. - Typing tips: use
xor*to multiply and/to divide; write 6.02 × 1023 as6.02 x 10^23or6.02e23. Rounding goes half up: 2.45 → 2.5.
Everything runs in your browser. What you type is saved on this device only.