How do I Measure the Size of Bacteria?

Bacteria are unicellular prokaryotes that have the potential to cause disease. A prokaryote is a type of cellular organism that does not possess a nucleus or complex organelles. Bacteria are microscopic and can therefore not be seen with the naked eye. Measuring the size of bacteria will help you to analyze and categorize various specimens.

Things You'll Need

• Microscope
• Ruler
• Pen
• Paper
• Calculator
• Bacteria

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Instructions

• 1

  Measure the diameter of the microscope's field of view. Using the low power objective, look through the microscope, and place the ruler under the field of view. Measure the diameter in millimeters. For example, you may find that the diameter of the field of view is five millimeters.

• 2

  Convert the measurement of the diameter from millimeters to micrometers. Bacteria are usually measured in small units, such as micrometers. There are 1,000 micrometers in one millimeter. If the diameter of the field of view is five millimeters, then multiply five by 1,000; the field of view is 5,000 micrometers in diameter.

• 3

  Observe the bacteria under the microscope with low power. Place the bacteria slide on the stage of the microscope, and then bring it into focus using the fine course adjustment knobs.

• 4

  Locate a single bacterium. The bacteria slide will typically have more than one bacterium. Find one bacteria, and then estimate how many times it will fit across the field of view. For example, you may find that a single rod-shaped bacteria will fit across the field of view about three times.

• 5

  Divide the diameter of the field of view by the number of times that the bacterium fits across the field of view. For example, if the diameter is 5,000 micrometers, and the bacteria fits across the field of view three times, then you divide 5,000 by three. In this case, the bacteria is approximately 1,667 micrometers.