Base64 Size Calculator
Base64 grows data by about 33%. Enter a byte size or a Base64 string length to see the other side, plus optional MIME (76) or PEM (64) line-break overhead—useful for e-mail limits, JWT budgets and data-URI CSS budgets.
Base64 size formula
Encoded length ≈ 4 × ceil(bytes / 3) characters. Padding uses = so the length is always a multiple of 4 (except most Base64URL and IMAP values, which omit padding).
- 1 KB → about 1,368 Base64 characters (~1.37×).
- 1 MB → about 1,398,104 characters before wrapping.
- MIME e-mail adds a CRLF every 76 characters on top of that.
When size matters in Europe and worldwide
Developers hit Base64 size limits in JWT cookies (often 4 KB), e-mail gateways, CDN header budgets, and GDPR-sensitive uploads where inlining a data URI avoids a network round-trip. Use this calculator before shipping large Base64 payloads.
سؤالات متداول
How much larger is Base64 than the original?
Exactly 4/3: every 3 bytes become 4 characters, so the Base64 string is about 33% larger, plus 0–2 "=" padding characters.
Do MIME or PEM make it even bigger?
Yes. Wrapping adds CRLF or LF every 76 (MIME) or 64 (PEM) characters, so long payloads grow a little more on top of the 33%.
Why do developers need a Base64 size calculator?
To check e-mail attachment limits, API payload caps, JWT cookie sizes, and whether inlining an image as a data URI will bloat CSS or HTML.
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