What This Calculator Does

Count significant figures, round to a target precision, or apply precision rules to two-number arithmetic. Target rounding accepts 1–15 figures and shows both ordinary decimal form and scientific notation with trailing zeros preserved. Use the rounding calculator for a fixed number of decimal places.

When to Use It

Check significant digits in a written measurement, round to three or another number of figures, or check arithmetic precision. Measurement uncertainty and full expressions are outside the model.

Inputs Explained

Keep the original spelling: 1.200 and 1.2 have the same value but different significant counts. Use dot decimals or e scientific notation with optional signs. The mantissa allows at most 100 digits, the exponent −100 to 100 and total input 120 characters. Non-finite values and nonzero inputs that underflow to zero are rejected. Thousands separators and comma decimals are unsupported.

Target precision must be a whole number from 1 to 15. Arithmetic also needs the second number and an operator; a divisor cannot be zero. Editing clears the old result. Calculating preserves URL parameters; existing count and operation shared links still restore.

How the Calculation Works

Leading zeros do not count; interior zeros do. A written decimal point preserves trailing zeros. Plain integers without a decimal point do not count trailing zeros. Scientific mantissas count explicitly written digits: 1200 has 2, 1200. has 4, 1.200e3 has 4 and 1200e3 also counts the four explicit mantissa digits.

Target rounding parses decimal strings directly, keeps the first N significant digits and increments when the next digit is at least 5. Midpoints round away from zero. A carry updates the exponent. Scientific notation keeps exactly N figures without converting back to a number and losing zeros.