Small calculators that show the working, so you learn the method and not only the answer. They run in your browser: nothing you type is sent to our servers.
Type an IPv4 address and a prefix length (for example 192.168.10.77/26). The calculator shows the subnet mask, the network address, the broadcast address, the first and last usable host and the number of usable hosts, with the binary working. The network address is the address with all host bits set to 0, the broadcast address has all host bits set to 1, and a prefix of /n leaves 32 minus n host bits, which gives 2 to the power of that many addresses (two fewer are usable for most prefixes).
Enter the supply voltage, the LED colour (forward voltage) and the current you want. The series resistor is R = (supply voltage minus LED voltage) divided by the current. The tool also suggests the next standard E24 resistor value, so you can pick a real part.
Convert between decimal, binary, hexadecimal and octal as you type, useful for addressing, masks, colours and low-level work.
Results are for learning and quick checks. Always check a datasheet or your network plan before building or changing anything real.