Hex Calculator - Add, Subtract, and Convert Hexadecimal

A hex calculator (hexadecimal calculator) adds, subtracts, multiplies, divides, and converts base-16 integers. Hex uses sixteen digits: 0 through 9 and A through F, where A is 10, B is 11, C is 12, D is 13, E is 14, and F is 15. People search for how to convert hex to decimal and how to add hexadecimal numbers because those two skills cover almost every CS homework problem that is not already binary.

Hex exists because humans are bad at reading long bit strings and machines are bad at decimal. One hex digit is exactly four bits: F is 1111, A is 1010, 0 is 0000. A byte is two hex digits, a 32-bit word is eight, a 64-bit address is sixteen. That grouping is why memory dumps, CSS colors, MAC addresses, and C integer literals all use hex instead of binary or decimal.

This free online hex calculator runs entirely in your browser with JavaScript BigInt. Nothing is uploaded. A 0x prefix is optional. Letters are case-insensitive: 0xa, 0xA, and A are the same input. Invalid digits such as G are rejected instead of being guessed. The hard limit is 64 hex digits (256 bits). That is enough for IPv6-sized integers and most crypto homework prefixes; it is not unlimited precision.

The default example is A + F = 19₁₆. In decimal that is 10 + 15 = 25, and 25 = 1×16 + 9, so the hex sum really is 19, not 15 and not AF. If your operands are already binary, use the binary calculator instead of translating every bit nibble by hand. For mixed scientific work that is not integer bases, a scientific calculator is the better sibling tool.

Using this hexadecimal adder and converter is straightforward:

1. Choose a mode. Convert shows hex, decimal, and binary for one integer. Add, Subtract, Multiply, and Divide take two hexadecimal integers.
2. Enter the number(s). Hex operands may look like A, 0xFF, or dead beef (spaces are stripped). Convert mode also lets you set the from-base to 16, 10, or 2.
3. Read the result panel. The primary display is uppercase hex. Decimal and binary sit underneath. Divide shows quotient and remainder (truncated toward zero).
4. Copy the hex string, or clear the fields. The last inputs are saved locally in your browser for up to 30 days.

Note: inputs and results are capped at 64 hex digits. Division by zero is an error. Subtracting a larger number from a smaller one yields a negative result shown with a minus sign in front of the magnitude. This is integer arithmetic only - no fractional hex, no IEEE floats, no two's-complement wrap of a fixed register width.

To convert hex to decimal, expand each digit as a power of 16. To add, work from the right and carry 1 for every 16 in a column - the same algorithm as decimal addition, with a larger digit set.

Example - add A + F (the default):

• A = 10 decimal, F = 15 decimal
• 10 + 15 = 25 decimal
• 25 = 1×16 + 9, so the hex result is 19
• Binary check: 1010 + 1111 = 11001, and 11001₂ = 19₁₆

Example - convert FF to decimal and binary:

• F×16¹ + F×16⁰ = 15×16 + 15 = 255
• Each F is 1111, so FF is 11111111 binary (one byte of ones)

Example - 10 + 10 in hex is not twenty:

• Hex 10 is decimal 16, so 10 + 10 = 20₁₆ = 32₁₀
• Writing 20 and reading it as twenty decimal is the usual off-by-base mistake. This calculator always labels the hex result and the decimal result separately.

Hex is a shorthand for binary, not a rival number system with different arithmetic. A + F in hex must match 1010 + 1111 in binary and 10 + 15 in decimal. If those three views disagree, a digit was misread. Convert mode on this page is there so you can catch that mismatch before you paste an address into a debugger.

The classic error is treating A + F as 15 because F looks like the "last" digit. F is 15, A is 10, and the sum is 25 decimal / 19 hex. Another error is assuming hex is case-sensitive. It is not: a and A are the same digit. This calculator accepts mixed case and prints uppercase so A–F do not look like 0–9 in a bad font.

A 0x prefix is decoration, not a multiply-by-something. 0x10 is sixteen, not "zero x ten." Putting 0b on a hex operand is invalid here; switch Convert to from-base 2 if the source is binary. G, H, and I are not hex digits - if a datasheet printed them, it was not hexadecimal.

People also confuse hex 10 with decimal 10. Hex 10 is 16. Hex 100 is 256. That power-of-sixteen pattern is the whole point of the notation, and it is the reason a two-digit color channel tops out at FF (255), not 99.

Hex multiplication is decimal multiplication with a different digit set. A × 2 = 14₁₆ because 10×2 = 20 decimal = 1×16 + 4. F × F = E1₁₆ because 15×15 = 225 decimal = 14×16 + 1. This calculator uses BigInt so you do not have to keep a 16-by-16 times table in your head, but the place-value story is the same as the addition example A + F = 19.

Hex division, like binary division, is integer quotient plus remainder. FF ÷ 10₁₆ is 255 ÷ 16, so the quotient is F and the remainder is F: 15×16 + 15 = 255. Division by zero is an error. Remainders are not hex fractions; 10 ÷ 3 is quotient 5 remainder 1 in decimal, which in hex is still quotient 5 remainder 1 because both 5 and 1 are the same glyphs in both bases.

Subtracting a larger hex integer from a smaller one produces a negative magnitude with a leading minus, not a wrap at 8 or 32 bits. If you needed (A − F) mod 100₁₆ for a two-digit color channel, that modular wrap is your extra step. The published cap is 64 hex digits - 256 bits - which is enough for a UUID-sized integer and not enough for a 2048-bit RSA modulus printed in full.

A nibble is four bits, and that is exactly one hex digit. That is the only reason hex beat octal in modern software. You can convert hex to binary by expanding each digit independently: A = 1010, F = 1111, so AF = 10101111. You cannot convert decimal to binary that way, because ten is not a power of two. Convert mode on this page will still do decimal ↔ hex ↔ binary for you; the nibble rule is why the binary column is easy to check by eye for hex input and hard to check for decimal input.

CSS colors, MAC addresses, and IPv6 pieces are hex because of this grouping, not because the underlying arithmetic is exotic. Adding two color channels can legally exceed FF; this tool will report 1FE for FF + FF and will not clamp. Memory addresses in a 64-bit process are up to sixteen hex digits. A 0x prefix does not change the value. Case does not change the value. G is never a hex digit.

If your homework is already in 0s and 1s, skip the nibble translation and use the binary calculator. If you need trig or a full expression line rather than integer bases, use a scientific calculator. This page stays honest: it is an integer hex tool with a 64-digit cap, not a debugger and not a color picker. People also search “convert hex to decimal” for values like 0xFF and “add hexadecimal numbers” for A + F; both are on this page, and both stay in the browser. Privacy is the same story as every other DevOkk math tool: after the script loads, a dropped network does not stop A + F from remaining 19 hex.