How many vertices should I use for a gun model in Unity 3d

I am wondering whether I should bump up the Subdivision modifier and have 21k Vertices or stay at 5k, I don’t know why there is such a big gap between 1 and 2.

every time you subdevide something you multiply the amount of faces by 4. so if you have 5k vereses then 21k verteses seems normal after 1 subdivision…

and if you should “bump up the subdivision” or not, depends on what the model will be used for. if its a game, then you should try not to use subsurface, or at least avoid it, and find alternative methods to smooth the mesh.

if its a CG animation, then use as many as you need, but not more, try to keep it as low as you can without losing details.

if its just to render a still image, then use as many as your computer can handle. if its ONLY the gun, then go to town on it as long as your system can handle it, if you will add lets say a scene, character, and other objects, then you should think how many verteses each objects should have.

all though its not necessary to use too many subdivisions since you wont really notice the difference when using smooth shading.