IP Subnet Calculator
Work out subnet details from an IP and mask — network address, broadcast, host range and count.
Making sense of a subnet
Given an IP address and a subnet mask or prefix, there is a set of facts a network engineer constantly needs: the network address, the broadcast address, the usable host range, and how many hosts the subnet holds. Calculating these by hand means fiddly binary arithmetic. This works them out for you, so you can plan or troubleshoot a network without reaching for a whiteboard.
Enter the IP and mask, and the subnet details are calculated.
Why the numbers matter
Subnetting is about dividing an address space into right-sized pieces, and getting it wrong wastes addresses or, worse, creates overlaps that break routing. The prefix length — the number after the slash — determines how many hosts fit, and the trade-off is fixed: a smaller network has fewer hosts but more networks. Seeing the host range and count spelled out helps you choose a mask that fits the number of devices without wasting the address space, which is the everyday craft of network design.
Questions & answers
What does the calculator tell me?
The network and broadcast addresses, the usable host range, and how many hosts the subnet holds, from an IP and mask.
What does the prefix like /24 mean?
It is the number of bits fixed as the network portion; the rest are for hosts, which sets how many devices the subnet holds.
Is anything uploaded?
No. The calculation happens in your browser.