Add two hexadecimal numbers exactly – columns carry at 16, so 8 + 9 writes 1 and carries 1, and the decimal cross-check confirms the result.
Show calculation steps
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Carrying at sixteen
Hex columns overflow at 16, not 10 — the single habit change from decimal addition. 8+9 writes 1 and carries 1 because 17 is 0x11; F+F writes E carry 1 because 30 is 0x1E. This page adds your operands with those rules and proves the result in decimal.
Address+offset is the daily use: base pointers plus struct offsets, section starts plus sizes, cursor positions in hex editors.
Worked example
ABC + 9F C+F = B carry 1 (27 = 0x1B) B+9+1 = 5 carry 1 (21 = 0x15) A+0+1 = B Sum: B5B (2748 + 159 = 2907 ✓)
| Example column | Result |
|---|---|
| 8 + 9 | 1 carry 1 (17 = 0x11) |
| C + 5 | 1 carry 1 (17 = 0x11) |
| F + F | E carry 1 (30 = 0x1E) |
| A + 4 | E, no carry |
The byte rollover
FF + 1 = 100 is the two-digit ceiling breaking — a carry rippling through a full byte. Watching it here is the hex view of overflow, and the mental model for why 0xFF boundaries matter in buffer maths.
Operand hygiene
Prefixes optional, case-insensitive, lengths may differ (short operands align at the ones place). Invalid characters are named with positions — the letter O and digit 0 confusion is caught, not guessed at.
Privacy
Addition happens in-page; addresses you paste are never transmitted.
Carrying at sixteen
Hex columns carry when they reach sixteen, so 9 + 8 writes 1 and carries 1, giving 0x11 — seventeen. Longer sums ripple the same way: 0xA8 + 0x64 is 0x10C, which the decimal cross-check confirms as 168 + 100 = 268. The letters make hand addition feel alien at first — you have to know instantly that C + 1 is D but F + 1 carries — and watching the column-by-column trace for your own operands is the quickest way to build that fluency.
How to use the Hex Addition Calculator
- Enter the two hex addends.
- Click "Add".
- The result is hex with a decimal cross-check line.
- Use uppercase or lowercase – both are accepted and the output case is switchable.
Frequently asked questions
How is hex addition different from decimal addition?
Only the carry threshold: columns carry at 16 instead of 10. ABC + 9F: C+F = 0x1B write B carry 1; B+9+1 = 0x15 write 5 carry 1; A+1 = B → B5B. Same algorithm, different base.
When do letters appear in a column result?
When the column total lands between 10 and 15 – A through F are ordinary digits. A column total of 16+ instead writes (total−16) and carries.
What everyday tasks are hex addition?
Address + offset (base pointer plus struct offset), summing byte lengths in a file layout, advancing through a memory map, and checksum arithmetic – the daily bread of debugging at the byte level.
Why does 0xFF + 0x1 = 0x100 feel special?
It is the byte rollover: 255+1 needs a ninth bit, so two hex digits become three. Watching FF roll to 100 is the hex view of a carry propagating through a full byte.
Do the operands need the same length?
No – shorter operands are implicitly left-padded. 0xABC + 0x9F aligns the 9F under BC.
How large can the addends be?
Unbounded – exact BigInt addition. Address-space-sized values (16 digits) are routine.
Is the sum computed locally?
Yes – in your browser, with nothing sent anywhere.
