Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Nikon AF-P DX 70-300mm F4.5-6.3G is the longer of the two lenses at 125mm. The Sigma 70-300mm F4-5.6 DG with a length of 122mm is 3mm shorter. On the other hand, the Sigma 70-300mm F4-5.6 DG has a larger diameter of 77mm compared to Nikon AF-P DX 70-300mm F4.5-6.3G's 72mm 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. Nikon AF-P DX 70-300mm F4.5-6.3G weighs 400g, which means it is 150g (37%) lighter than the Sigma 70-300mm F4-5.6 DG which has a weight of 550g.
Both Nikon AF-P DX 70-300mm F4.5-6.3G has the Nikon F (DX) lens mount whereas the Sigma 70-300mm F4-5.6 DG has the Nikon F (FX) lens mount. Some of the latest released cameras that are compatible with these mounts are Nikon D3500, Nikon D7500 and Nikon D5600 for the Nikon F (DX) Mount and Nikon D6, Nikon D780 and Nikon D3500 for the Nikon F (FX) Mount.
Sigma 70-300mm F4-5.6 DG is also available in Canon EF , Nikon F (FX), Pentax KAF, Sony Alpha, Sigma SA, Canon EF, Pentax KAF, Sony Alpha and Sigma SA mounts.