Rounding & Significant Figures Calculator

Decimal places, significant figures and multiples

Rounding replaces a number with a simpler one that is close to it. Rounding to decimal places keeps a fixed number of digits after the decimal point: 3.14159 to two decimal places is 3.14. Rounding to significant figures keeps a fixed number of meaningful digits regardless of where the decimal point is: 0.0045678 to three significant figures is 0.00457 and 123,456 becomes 123,000. Significant figures are the standard way to express precision in science and engineering, because they reflect how accurately a value was measured.

Rounding to the nearest multiple snaps a value to a grid. Prices are often rounded to the nearest 0.05 or 0.10 when small coins are not used, times to the nearest 15 minutes, and quantities to the nearest 10 or 100. The calculator accepts any positive multiple. It also shows the result in scientific notation and counts the significant figures in your input, flagging integers like 1200 whose trailing zeros are ambiguous.

Rounding rules explained

The rule only matters when the digits being dropped are not zero. Half up is the method taught in school: 5 and above rounds away from zero. Half to even, or banker's rounding, sends exact halves to the nearest even digit, which keeps sums of many rounded values unbiased. Half down rounds exact halves toward zero. Ceiling always rounds toward positive infinity, floor toward negative infinity, and truncate simply cuts off the extra digits.

Unlike a typical spreadsheet or programming language, this calculator works with exact decimal digits instead of binary floating-point numbers. That means values such as 1.005, 2.675 or 0.125 round exactly as written, and very long numbers keep every digit. The table under the result shows the same number at several precisions so you can pick the one that fits your report. Everything runs locally in your browser.