Bit/Register Calculator

About this tool

Click any bit to set, clear, or toggle it, and watch the decimal, hex, and binary representations update instantly — the everyday task of figuring out what value to write to a microcontroller register to turn specific bits on or off. Type a value directly (hex, binary, or decimal) to load it into the bit grid instead.

Frequently asked questions

Which end is bit 0?

Bit 0 (the least significant bit) is on the right, matching how binary numbers are normally written and read — the leftmost bit is the most significant bit (bit 7, 15, or 31 depending on width).

How do I enter a value?

Type it with a prefix: 0x1F for hex, 0b00011111 for binary, or just 31 for decimal — the bit grid and other formats update as soon as it parses.

What happens if I switch register width after setting bits?

The current decimal value carries over and is re-rendered into the new bit width — switching to a narrower width truncates any bits beyond the new width, since they no longer exist in the register.