Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Canon 24-105mm F3.5-5.6 IS STM is the longer of the two lenses at 104mm. The Canon 24-85mm f3.5-4.5 USM with a length of 70mm is 34mm shorter. Besides being longer, the Canon 24-105mm F3.5-5.6 IS STM also has a larger diameter of 83mm compared to Canon 24-85mm f3.5-4.5 USM's 73mm diameter.
Weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Canon 24-85mm f3.5-4.5 USM weighs 380g, 38% (145g) lighter than the Canon 24-105mm F3.5-5.6 IS STM's weight of 525g.
Below you can find the dimension and weight table of the 'Standard Zoom Lenses in Canon EF Mount for size comparison purposes.
Standard Zoom Lenses in Canon EF Mount for Size Comparison
Lens Mounts
Both Canon 24-105mm F3.5-5.6 IS STM and Canon 24-85mm f3.5-4.5 USM has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Focal Range
Canon 24-105mm F3.5-5.6 IS STM has a focal range of 24-105mm and 4.4X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 38.4 - 168mm.
Canon 24-85mm f3.5-4.5 USM has a focal range of 24-85mm and 3.5X zoom ratio . When it is mounted on an APS-C sensor camera with 1.6x crop, it provides an 35mm (FF) equivalent of 38.4 - 136mm.