Enter an IP with its CIDR prefix into a browser-based subnet calculator and it shows the total number of usable host addresses in that block. The count excludes the network and broadcast addresses automatically, and everything is computed on your device.
A subnet has two to the power of its host bits total addresses, but two of them are reserved: the network address and the broadcast address. So the usable host count is that total minus two. For a /24 that is 256 total and 254 usable. A subnet calculator applies this rule for any prefix so you do not have to remember the off-by-two.
Because the calculator runs in your browser, you can size subnets for a private network without sending your plan to any server. Enter the prefix you are considering, read the usable host count, and adjust the prefix until the block is the right size. It is free and needs no sign-up.
The network and broadcast addresses are reserved, so they are subtracted from the total.
A /24 has 256 total addresses and 254 usable host addresses.
No. The count is calculated locally in your browser.