Enter IPv4 CIDR details
Use CIDR notation directly, or enter an IP and prefix separately. The calculator shows routing, capacity, and binary results.
Formula used
Subnet mask from prefix: A prefix of /n keeps n network bits at 1 and the remaining bits at 0.
Network address: Network = IP AND SubnetMask
Broadcast address: Broadcast = Network OR WildcardMask
Total addresses: 2^(32 - prefix)
Usable hosts: Standard subnets use Total - 2. This page treats /31 as two usable point-to-point addresses and /32 as one host route.
Remaining assignable addresses: UsableHosts - ReservedIPs
How to use this calculator
- Enter a CIDR block like
10.20.30.40/22, or provide the IP address and prefix separately. - Add reserved IPs when you want a planning number for truly assignable addresses.
- Press Calculate CIDR Block to show the results above the form.
- Review network, broadcast, host range, mask, class, scope, and binary outputs.
- Download the results as CSV or PDF for documentation, audits, or project handoffs.
Example data table
| CIDR Block | Subnet Mask | Total Addresses | Usable Hosts | First Host | Last Host |
|---|---|---|---|---|---|
| 192.168.1.10/24 | 255.255.255.0 | 256 | 254 | 192.168.1.1 | 192.168.1.254 |
| 172.16.5.129/27 | 255.255.255.224 | 32 | 30 | 172.16.5.129 | 172.16.5.158 |
| 10.0.0.2/30 | 255.255.255.252 | 4 | 2 | 10.0.0.1 | 10.0.0.2 |
FAQs
1. What does a CIDR prefix mean?
A CIDR prefix tells you how many leading bits belong to the network. A larger prefix means fewer host bits, fewer total addresses, and a smaller subnet.
2. Why do network and broadcast addresses matter?
They define the edges of the subnet. The network address identifies the block, and the broadcast address reaches all hosts inside that block.
3. How is usable host count calculated?
Most IPv4 subnets reserve the network and broadcast addresses, so usable hosts equal total addresses minus two. This calculator also supports /31 and /32 edge cases sensibly.
4. What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. Routing tools and access control entries often use it to match address ranges quickly.
5. Why include reserved IPs?
Reserved IPs help with planning. You can subtract gateways, firewalls, management interfaces, or fixed devices to estimate how many addresses remain assignable.
6. Can this tool identify private versus public addresses?
Yes. It checks standard IPv4 ranges and labels the address scope as private, public, loopback, link-local, multicast, carrier-grade NAT, or reserved.
7. Why show binary values?
Binary output makes subnet logic easier to verify. You can see exactly where network bits stop and host bits begin for the IP, mask, network, and broadcast values.
8. When should I export the results?
Exporting helps when you need documentation, project records, review notes, or handoff material for network builds, migrations, audits, and troubleshooting sessions.