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Base64 Decode

Decode any Base64 string back to text instantly — UTF-8 safe. Free, fast, no sign-up.

Last updated: October 2026

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How Base64 decoding works

Base64 text is split into groups of 4 characters.
Each group becomes 3 bytes (6 bits per character).
The bytes are read back as UTF-8 text.

Example: "SGk=" → 48 69 → "Hi".

Background reading: the Base64 encoding scheme on Wikipedia.

Base64 alphabet

The 64 characters of the Base64 alphabet and their 6-bit values (0–63) — decoding maps each character back to its value.

Char	Value	Char	Value	Char	Value	Char	Value
A	0	B	1	C	2	D	3
E	4	F	5	G	6	H	7
I	8	J	9	K	10	L	11
M	12	N	13	O	14	P	15
Q	16	R	17	S	18	T	19
U	20	V	21	W	22	X	23
Y	24	Z	25	a	26	b	27
c	28	d	29	e	30	f	31
g	32	h	33	i	34	j	35
k	36	l	37	m	38	n	39
o	40	p	41	q	42	r	43
s	44	t	45	u	46	v	47
w	48	x	49	y	50	z	51
0	52	1	53	2	54	3	55
4	56	5	57	6	58	7	59
8	60	9	61	+	62	/	63

Base64 decoding in code

Python

import base64
base64.b64decode("SGkg8J+Riw==").decode()
# → 'Hi 👋'

JavaScript

decodeURIComponent(escape(atob("SGkg8J+Riw==")));
// → 'Hi 👋'

C

/* C has no standard-library Base64 decoder. The usual approach
   is the reverse of encoding:
   1. Map each of the 4 input characters back to its 6-bit value
      using the alphabet "ABC...Zabc...z0-9+/".
   2. Regroup the 6-bit values into bytes: 4 chars -> 3 bytes.
   3. Strip '=' padding. Example: "SGk=" -> S=18, G=6, k=36
      -> bytes 0x48 0x69 -> "Hi". */

Common values

SGk= → “Hi”
TWFu → “Man”
QQ== → “A”
QUI= → “AB”

Key takeaways

Decoding reverses encoding: 4 Base64 characters → 3 bytes.
Stray characters or bad padding cause ‘invalid Base64’ errors.
Decoded bytes are not always text — they can be images or files.
Base64 offers no security; treat decoded content with care.

Frequently asked questions

How do I decode Base64?

Paste the Base64 string above — the decoder handles the rest, including '=' padding.

Why does my Base64 end with '='?

'=' is padding added when the input length isn't a multiple of 3 bytes.

I get an error — why?

Base64 only uses A–Z, a–z, 0–9, +, / and '=' padding. Other characters mean the string is damaged or incomplete.

What does ‘invalid Base64’ mean?

The input contains characters outside the Base64 alphabet, or the padding is wrong — check for spaces or missing = signs.

Can I decode Base64 without padding?

Often yes — the decoder can infer missing = padding from the string length.

Why is my decoded text garbled?

It was probably encoded from raw bytes (like an image), not text — decoding those bytes as text gives mojibake.

Is decoding Base64 safe?

Decoding is safe, but the result can be anything — an image, a file, or text. Do not execute decoded content you do not trust.

Need to encode? Try our Base64 encoder.

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Char	Value	Char	Value	Char	Value	Char	Value
A	0	B	1	C	2	D	3
E	4	F	5	G	6	H	7
I	8	J	9	K	10	L	11
M	12	N	13	O	14	P	15
Q	16	R	17	S	18	T	19
U	20	V	21	W	22	X	23
Y	24	Z	25	a	26	b	27
c	28	d	29	e	30	f	31
g	32	h	33	i	34	j	35
k	36	l	37	m	38	n	39
o	40	p	41	q	42	r	43
s	44	t	45	u	46	v	47
w	48	x	49	y	50	z	51
0	52	1	53	2	54	3	55
4	56	5	57	6	58	7	59
8	60	9	61	+	62	/	63

Char	Value	Char	Value	Char	Value	Char	Value
A	0	B	1	C	2	D	3
E	4	F	5	G	6	H	7
I	8	J	9	K	10	L	11
M	12	N	13	O	14	P	15
Q	16	R	17	S	18	T	19
U	20	V	21	W	22	X	23
Y	24	Z	25	a	26	b	27
c	28	d	29	e	30	f	31
g	32	h	33	i	34	j	35
k	36	l	37	m	38	n	39
o	40	p	41	q	42	r	43
s	44	t	45	u	46	v	47
w	48	x	49	y	50	z	51
0	52	1	53	2	54	3	55
4	56	5	57	6	58	7	59
8	60	9	61	+	62	/	63