Magnification Calculator

Total Microscope Magnification

Total magnification = objective lens magnification × eyepiece (ocular) magnification.

The Magnification Formula

Magnification describes how many times larger an image of an object appears compared to its real (actual) size. It is a ratio, so it has no units, and is usually written with a multiplication sign, such as ×100.

Rearranging the same equation lets you solve for either size:

• actual size = image size ÷ magnification
• image size = magnification × actual size

The image size and actual size must be expressed in the same unit of length (for example both in millimeters or both in micrometers) so that the units cancel and the magnification is a pure number.

Drawing and Photo Magnification

In biology you often calculate the magnification of a scientific drawing or a micrograph rather than the magnification of the microscope itself. To do this, measure the size of a feature on the drawing or photo (the image size) and compare it to the real size of that feature (the actual size).

• Measure the image with a ruler, then convert to a single common unit (1 cm = 10 mm = 10,000 µm).
• If a cell drawn 40 mm wide is really 0.5 mm wide, the magnification is 40 ÷ 0.5 = ×80.
• Always check that a scale bar or stated actual size uses the same unit before dividing.

Total Magnification (Objective × Eyepiece)

A compound light microscope magnifies in two stages. The objective lens closest to the specimen produces an enlarged image, and the eyepiece (ocular) lens magnifies that image again for your eye. The overall magnification is the product of the two:

• A ×10 eyepiece with a ×4 objective gives ×40 total.
• A ×10 eyepiece with a ×40 objective gives ×400 total.
• A ×10 eyepiece with a ×100 oil-immersion objective gives ×1000 total.

Related Calculators