-snip-
here is an example for your curiosity 52135 (bytes)

I think with "advanced view" its more clear.

-> https://blockchain.info/tx/ef492f5dd516f51061a77bc148b8925e74557b1f31a42ca51098f26b82c23fb0?show_adv=true

Every input (shown on the left) needs ~148 (or 180[1]) bytes and this TX has 290 inputs. 290*180 = 52 200 ~= 52 135.

[1] for uncompressed pubkeys as in this example.