The place value of a digit within a decimal (base 10) number is determined by its relative location to the decimal point. The digit to the left of the decimal point occupies the ones place value, and each place value continuing to the left increases by a factor of 10. Therefore, the number 293 has three digits with the three occupying the ones place value, the nine occupying the tens place value, and the two occupying the hundreds place value. The greatest place value in a number is the digit farthest to the left. Rounding numbers, especially large numbers, to the greatest place value allows numbers to be more easily conceptualized and manipulated (2,000,000 is easier to work with than 1,947, 314).

Find the farthest left digit in the number. This number occupies the greatest place value. For example, in the number 536, the number five is the farthest left and occupies the greatest place value--in this case hundreds.

Find the digit to the immediate right of the leftmost digit. If the number is five or more, add one more to the leftmost digit. If the number is four or less, leave the leftmost digit as is. Continuing the example, the digit to the right of the five in the number 536 is three. Since this number is four or less, the leftmost digit remains five. As a second example, in the number 879 the leftmost digit is eight and the digit to the immediate right is seven. Since the number to the right is five or more, the eight is rounded up to nine.

Replace the digits following the rounded greatest place value with zeros. For the rounded numbers in the previous example, the number 536 is rounded to 500 and the number 879 is rounded to 900.