Macro Magnification Calculator
Calculate magnification (reproduction ratio) from subject size on the sensor versus real subject size, or from extension.
Inputs
Results
What is magnification?
Magnification (reproduction ratio) is how large the subject is projected on the sensor compared with its true size. 1× or 1:1 means life-size on the sensor — a 20 mm insect spans 20 mm on the sensor.
Formulas
The extension formula is an approximation for a thin lens focused at infinity before adding tubes. True magnification also depends on focus distance and complex lens designs.
FAQ
Does crop factor increase magnification?
Crop factor changes field of view, not optical magnification on the sensor. A 1:1 lens remains 1:1 on APS-C; you simply frame a tighter portion of the scene.
Why is depth of field so thin in macro?
Effective aperture increases with magnification, and focus distances are tiny. Use the DOF calculator with short subject distances to see how narrow the sharp zone becomes.
Macro exposure and DOF notes
As magnification rises, effective f-number increases and light drops. Diffraction appears earlier, and DOF may span only millimeters. Focus stacking and rail movements become practical tools once you see magnification cross 1:1. Extension-tube estimates are approximate—confirm with a ruler on the subject plane.