How to get right object proportions from single photo?

How to get right proportions of object from single photo taken from the side? I always get complaints about misproportions of objects i create, in those cases i don’t have proper reference images to get it right, they’re taken from different sides and with low focal length

I virtually any case when looking for references there is far more than one image file.

If you could give us an example of something we may be able to help a bit better…
I general… a full search can yield the actual dimensions of an object…even if you only find the dimensions of a part that makes up that object you can divide a way to find overall dimensions using the part as a unit of measure…