Learn the hex digits for 0–15 by heart
The 16 hex digits and their decimal/binary equivalents: 0=0000, 1=0001, 2=0010, 3=0011, 4=0100, 5=0101, 6=0110, 7=0111, 8=1000, 9=1001, A=1010, B=1011, C=1100, D=1101, E=1110, F=1111. Knowing these lets you convert hex to binary and back mentally — each hex digit is exactly four binary bits.
Hex colour codes — understanding the structure
A six-character hex colour #RRGGBB splits into three two-digit hex pairs. #FF6B6B = R:FF(255) G:6B(107) B:6B(107). Two identical hex digits always give a range from 0 (00) to 255 (FF). A shorthand three-character code #RGB expands by doubling each digit: #F6B = #FF66BB. Useful to know when reading design tokens or debugging CSS variables.
Unix permissions in octal
chmod uses octal because three bits map perfectly to read (4), write (2), execute (1). Adding these values gives 0–7 for each of the three permission groups (owner, group, others). chmod 644 = owner:6(rw-) group:4(r--) others:4(r--). chmod 755 = owner:7(rwx) group:5(r-x) others:5(r-x). The converter shows the binary equivalent, which makes the bit structure immediately visible.
Check if a number is a power of 2 in binary
Powers of 2 always appear as a single 1 followed by zeros in binary: 1, 10, 100, 1000, 10000... (1, 2, 4, 8, 16...). If you need to check whether a number is a power of 2 in code, the classic bit trick is (n & (n-1)) === 0 — visible immediately if you convert both n and n-1 to binary and see the pattern.