Rounding & Significant Figures Calculator

Round a number to a place value, decimal places, or significant figures. Enter one number, choose the target, and select Round to see the result and the digit used in the decision.

Rounding calculator

Rounding examples

• 6.7197 to 2 significant figures: keep 6 and 7; the next digit is 1, so the result is 6.7, displayed as 6.7 × 10^0.
• 65378 to 2 significant figures: keep 6 and 5; the next digit is 3. The result is 65000, displayed as 6.5 × 10^4 to make the two significant digits clear.
• 0.00456 to 2 significant figures: leading zeros do not count. Keep 4 and 5, then use the next digit, 6, to obtain 0.0046, or 4.6 × 10^-3.
• 9.99 to 2 significant figures: carrying produces 10. The display 1.0 × 10^1 preserves exactly two significant digits.

Decimal places and significant figures

Decimal places count digits after the decimal point. Significant figures count from the first nonzero digit. For example, 0.00456 to two decimal places is 0.00; to two significant figures it is 0.0046. Choose the mode that matches your assignment.

Significant-figure results use scientific notation so trailing zeros are unambiguous: 100 to three significant figures is 1.00 × 10^2. Adding zeros to a display does not make a measured value more accurate.

Rounding rules and input limits

This tool rounds to the nearest target, with exact halfway cases going away from zero: 2.5 becomes 3 and -2.5 becomes -3. For negative numbers, an increased magnitude means moving farther from zero. Some science and measurement instructions use ties-to-even instead; follow the convention your assignment specifies.

Enter one decimal number, optionally in e notation such as 1.25e-6. Expressions, fractions, commas, and units are not inputs. Custom precision accepts 0–20 decimal places or 1–20 significant figures. Input is limited to 100 digits and a decimal exponent between -100 and 100. For zero in significant-figure mode, displayed zeros are a formatting convention rather than a claim about measurement precision.

Round once from the original value. Rounding an intermediate result can change a later answer. The calculator shows the retained place and the next digit; compare those steps with your own work.

Count the significant figures in a number

Need to know how many significant figures a number already has, rather than round it? Enter it in the significant figures counter below. It applies the rules listed underneath and flags ambiguous values such as 1200.

The significant-figure rules

• All nonzero digits are significant.
• Zeros between nonzero digits are significant: 405 has three.
• Leading zeros are never significant: 0.0045 has two.
• Trailing zeros are significant only when a decimal point is shown: 100.00 has five, while 1200 written without a decimal point is ambiguous.

Example: 0.004560 has four significant figures, the 4, 5, 6 and the final zero, which counts because the number has a decimal point.

Practice before checking

Try 1846, 5972, and 4361 to two significant figures. The results are 1800 (1.8 × 10^3), 6000 (6.0 × 10^3), and 4400 (4.4 × 10^3).

For more guided practice, read the rounding numbers lesson. For measurement conventions and significant zeros, see OpenStax’s explanation of significant figures; its exact-halfway convention differs from this tool.