Interactive calculator
Round to significant figures
3500
35.0056
3.5e3Three-part reference
Understand the number before you round it.
Each section answers one question: what significant digits mean, how the common method behaves, and when NIST SP 811 produces a different result.
The foundation
Rounding significant digits
Significant digits communicate precision. Begin counting at the first nonzero digit, keep the requested number of digits, and use the next digit to decide whether the final retained digit changes.
- 1–9 Nonzero digits always count
- 0 Interior zeros count
- .007 Leading zeros do not count
- 380.0 A decimal makes trailing precision explicit
COMMON
Common method
This familiar classroom method looks at the first discarded digit. A digit below 5 leaves the retained digit unchanged; a digit of 5 or greater increases it by one.
Metrology standard
NIST SP 811 method
NIST treats an exact halfway value differently. When the discarded digits are a 5 followed only by zeros, the retained digit is left unchanged if even and increased if odd.
The one important difference