Comparison of Two Apparent Sizes

Calculator for angular diameter or apparent size of two objects and comparison of the sizes. The angular diameter is calculated from the actual size and distance. See there for the formula to calculate it.
Please enter the values ​​size and distance for two objects to calculate a comparison of the angular diameters and thus the apparent sizes.

Size objekt A:		millimeters, mmcentimeters, cmdecimeters, dmmeters, mkilometers, kminches, in, ″feet, ft, ′yards, ydmiles, mi
Distance objekt A:		millimeters, mmcentimeters, cmdecimeters, dmmeters, mkilometers, kminches, in, ″feet, ft, ′yards, ydmiles, mi
Size objekt B:		millimeters, mmcentimeters, cmdecimeters, dmmeters, mkilometers, kminches, in, ″feet, ft, ′yards, ydmiles, mi
Distance objekt B:		millimeters, mmcentimeters, cmdecimeters, dmmeters, mkilometers, kminches, in, ″feet, ft, ′yards, ydmiles, mi
Decimal places: 0 1 2 3 4 5 6
Angular diameter objekt A:		°
Angular diameter objekt B:		°

Objekt A appears times as large as objekt B.
Objekt B appears times as large as objekt A.

Example: the thumb is 2.5 cm wide and 60 cm from the eye. The moon is 3474 km wide and has an average distance of 384400 km. This makes the thumb appear 4.6 times larger.

The size of an object here refers to its visible diameter. With long or flat objects, it is possible that they won't show us their longest sides. Spherical objects, on the other hand, like the full moon in the example above, appear the same size from every direction. If a non-spherical object is tilted towards the observer and you want to know its true length, you have to divide the measured length by the sine of the tilt angle. This tilt angle is 90 degrees when viewed perpendicularly, and the sine is 1 then. Otherwise, it is smaller, and if you divide by a value less than 1, the result becomes larger. This applies theoretically to one-dimensional objects. For real-world objects, it is a bit more complicated, because you have to find the correct points for the measurement.

How large something appears depends essentially on two factors equally: its actual size and its distance. Therefore, one cannot infer its true size from its apparent size alone. Humans, however, have two eyes, which provide spatial vision. This is extremely precise up to a distance of 10 meters and still delivers good stereoscopic impressions up to 100 meters. Beyond several hundred meters, it ceases to function properly. For objects at greater distances, experience plays a significant role. We have a general idea of ​​the size of trees, houses, mountains and similar objects. Depending on atmospheric conditions, distant objects become fainter and less contrasty over time, which also influences our perception of distance. However, these factors can be deceptive.

Last updated on 01/19/2026. Author: Jürgen Kummer

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