same pixel sizes appears in different size in two webpages in same device?

I am trying to clone as website but i am facing an issue, i am giving same pixels what is given in original website but size appearance in my website is bigger, i am using same font family as well, this issue is for fonts and dimensions as well. for example:

1. font size is 50px in original website so i gave 50px in my website but text size in my website is bigger than original website
2. div width is 100px in original website so i gave 100px in my website but mine appear wider than original.

can someone help my what is that i am missing? what is the reason for this?