linux file permission simplest rule of thumb

Chmod 777 –R /var/www/html/webdir
Permission level
1.       r (read)       =  4
2.       w (write)     =  2
3.       x (execute)  =  1

For example : 

chmod 753 abc.txt thus means
assign (4+2+1)(4+1)(2+1) to abc.txt

=>
assign (rwx)(rx)(wx) to abc.txt
assign (owner)(group)(other) to abc.txt

Another example

chmod 572 dump.txt thus means
assign (4+1)(4+2+1)(2) to 
dump .txt
=>
assign (rw)(rwx)(w) to  dump .txt