Hex transparency in colors [duplicate]

Question

I'm working on implementing a widget transparency option for my app widget although I'm having some trouble getting the hex color values right. Being completely new to hex color transparency I searched around a bit although I couldn't find a specific answer to my question.

I want to set transparency by hex color so let's say my hex color id "#33b5e5" and I want it to be 50% transparent. Then I'll use "#8033b5e5" because 80 is 50%.

I found a useful chart here: http://www.dtp-aus.com/hexadeci.htm . With this data I managed to come up with this:

0% = #00 10% = #16 20% = #32 30% = #48 40% = #64 50% = #80 60% = #96 70% = #112 80% = #128 90% = #144 

Now the issues start appearing when I get higher than 100 in hex. Hex color codes can only be 8 symbols long right? For example #11233b5e5 (80%) crashes.

What can I do to enable me to use the higher numbers aswell?

Answer 1

Here's a correct table of percentages to hex values for opacity. E.g. for 50% white you'd use #80FFFFFF. To think in terms of transparency instead, flip the order of the percentages (more opaque = less transparent).

%	Hex
100%	FF
95%	F2
90%	E6
85%	D9
80%	CC
75%	BF
70%	B3
65%	A6
60%	99
55%	8C
50%	80
45%	73
40%	66
35%	59
30%	4D
25%	40
20%	33
15%	26
10%	1A
5%	0D
0%	00

(source question)