IP Range Calculator
About the IP Range Calculator
The IP Range Calculator converts between different ways of expressing a block of IP addresses, computing the first and last address, the total count, and the equivalent CIDR or netmask representation. Give it a start and end address, a CIDR block like 10.0.0.0/22, or an address-plus-mask, and it returns the boundaries and size of the range so you can reason about contiguous blocks of addresses rather than a single subnet.
An IP range is defined by its lowest and highest addresses; in CIDR form a shorter prefix covers exponentially more addresses, since each bit dropped from the prefix doubles the count. The tool handles the arithmetic of mapping an arbitrary start-end pair to the smallest set of CIDR blocks that cover it, which matters because access lists, route tables, and cloud security groups usually require CIDR notation rather than free-form ranges.
Engineers use this to define firewall and security-group allowlists, plan DHCP scopes, summarize routes, audit which addresses fall inside a block, and translate a vendor-supplied range into the CIDR format a router or cloud console demands. It is also useful for verifying that an address you are about to assign sits inside the intended allocation.
A practical tip: not every start-end range maps to a single clean CIDR block, so a range may need several CIDR entries to cover it exactly without including extra addresses. When you are working within one subnet and need the network, broadcast, and host details, the Subnet Calculator is the closer fit, while this tool shines for spanning, comparing, and aggregating blocks.
Frequently asked questions
- What is the difference between this and the Subnet Calculator?
- The Subnet Calculator focuses on a single subnet's network, broadcast, and host details. The IP Range Calculator works with arbitrary start-to-end blocks and converts them to and from CIDR.
- Why might one IP range need several CIDR blocks?
- CIDR blocks must align to power-of-two boundaries. An arbitrary start-end range that does not align is covered by combining multiple CIDR blocks of different sizes to include every address and nothing extra.
- How many addresses are in a /22 block?
- A /22 contains 1,024 addresses (four /24 networks), because 32 minus 22 leaves 10 host bits and 2 to the 10th power is 1,024.
- Can I use the output directly in a firewall rule?
- Yes. Most firewalls, cloud security groups, and routers expect CIDR notation, which is exactly what the calculator produces from a start-end range or a mask.