Surprise Attack Macro / Guarantee Crit

Hey Guys, in my campaign i have an assasin. Is there any way to build a macro or something for the Assasination / Guarantee Crit thing? Like when he surprise an enemy he 100% crits with his first hit. How can i Build a macro which Does a hit with his weapon + sneak etc. and 100% crit? Hope u know what i mean :) Thanks!

What game are you playing and which character sheet are you using? 

Hey, sorry! DnD 5e with the standard Char Sheet from Roll20

Hi A B.,  Assuming you mean "D&D 5e by Roll20" as the character sheet (there are seven D&D 5e character sheets) then a macro is not necessary here, you can change the attack's critical value to 2. That will replicate what you want to do.  Here is an example of the complete setup. (Example uses Rapier) Note that the Sneak attack calculation is: [[ceil(@{level}/2)]]d6

Wow Thanks! That was easy :D The Sneak Attack calculation Stays the same? Eben on higher Levels?

Yes, ceil(level/2) will give you a d6 every odd level, just like the chart shows.  ceil(1/2) = 1 ceil(2/2) = 1 ceil(3/2) = 2 ceil(4/2) = 2 ceil(5/2) = 3 and so on. 

Thank you very much, thats all i need - and its rly easy :)