Using the ruler, measure the length and width of the area in which you would like to center the object. For example, if you are centering a picture on a wall, measure the length of the wall, and the height from floor to ceiling. If you are centering an item on a page, measure the length and width of the page. Apply this concept to any area in which an item needs centering.
Write down the measured length and width.
Using the calculator if necessary, divide the length in half and write down the result. Repeat for the width.
Measure the resulting length from one side of the wall, page or area to the determined midway point.
Mark this distance on the wall, page or area.
Measure the resulting width from the floor, ceiling or side of the page or area. Align with the mark where you measured for the length.
Mark this width. This mark represents the center point.