This is a simple trigonometric calculation: the height of an image divided by the height of the object. In this case, it’s 3 ÷ 1 = 3. Yep, it’s a simple trigonometric calculation. If an object is one inch tall and its inverted image is three inches tall, then the magnification would be two (because 12 ÷ 32 = 0.33).
What if they’re both four feet tall?
In that case, you can use this equation: height of object divided by height of image – dividing gives the answer in meters or centimeters; multiplying will give it in millimeters or inches. So for example with our previous calculations we could do this: 1200 ÷ 2400 which equals .50 (0.50 cm per mm) so there are 50 lines to each line on the paper or rather than writing “height” as 1200 here we can write “1200 mm” and “height of object divided by height of image”.
In this case, it’s 2400 ÷ 1200 = .50 (0.50 cm per mm) so there are 50 lines to each line on the paper–or rather than writing “height” as 2400 here we can write “2400 mm”. The magnification would be two! The next few sentences should discuss how a person could use this information to calculate the size in millimeters or inches for an item they’re looking at that has been photographed using their phone.