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Putting sizes in perspective

Hair and red blood cell: comparing two diameters

The hair’s diameter is compared with that of a red blood cell. The drawn hair fragment’s length is not part of the calculation.

Human hair: a dimension about 9.333 times that of Red blood cell using the adopted values.

Try this comparison

How many red blood cell diameters make up a hair’s diameter?

Dimensions adopted for the calculation
ReferenceDimension
Human hair70 µm
Representative diameter
Red blood cell7.5 µm
mean diameter

Calculation: 70 µm ÷ 7.5 µm, after conversion into the same unit. The ratio calculated from the catalogue data is about 9.333.

Both illustrations use a common factor for the stated dimension. Positions aid reading and do not represent physical separation.

Check the conventions

Human hair

Hair thickness varies greatly between individuals. Displayed dimension: representative diameter.

Catalogue value to check against the source; not individually audited.

Red blood cell

A flexible biconcave disc adapted to carrying oxygen. Displayed dimension: mean diameter.

Dimension checked in a primary source that was consulted.

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Replace an object in the explorer, keep the common scale factor and try predicting the new ratio before reading it.

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