IP Subnet Calculator Online – IPv4 CIDR, Subnet Mask and Host Range
Subnet Calculator
Use this free IP subnet calculator online to work out IPv4 network addresses, usable IP ranges and subnet masks instantly.
Quick answer
To use this IP subnet calculator online, type an IPv4 address such as 192.168.1.130 and choose a CIDR prefix from /1 to /32, for example /26 (255.255.255.192). The results update instantly: network address, broadcast address, usable host range, subnet mask, wildcard mask, total IPs, usable hosts, IP class, and the mask and address in binary. Invalid addresses are flagged under the input.
Subnetting splits a network into smaller blocks, and getting the maths wrong can leave devices unable to talk to each other. This free IP subnet calculator online does the binary arithmetic for you. Enter an IPv4 address and a prefix length and you immediately see the network boundaries, the range of usable addresses and the matching masks.
I checked the results against standard subnetting tables, including the special /31 point-to-point and /32 single-host cases, which many calculators get wrong. It is useful for network engineers, students preparing for CCNA or Network+ and anyone configuring routers, firewalls or cloud VPCs.
IP Subnet Calculator Online Features
| Feature | How it works |
|---|---|
| Any IPv4 address | Works with private and public IPv4 addresses |
| All prefixes /1 to /32 | Each option shows the dotted subnet mask next to the CIDR |
| Network and broadcast | Shows the first and last address of the subnet |
| Usable host range | First and last assignable host addresses |
| Masks | Subnet mask and wildcard (inverse) mask for ACLs |
| Host counts | Total IPs and usable hosts, with /31 and /32 handled correctly |
| Binary view | Binary subnet mask and binary IP address |
| Instant and private | Updates as you type and runs locally |
How to Use the IP Subnet Calculator Online
Step 1: Enter an IPv4 address
Type any address from the network you are planning, for example 192.168.1.130. It does not need to be the network address; the calculator works out the boundaries for you. If the address is not valid IPv4, an error message appears below the box.
Step 2: Choose the CIDR prefix or subnet mask
Open Network Mask / CIDR and pick the prefix length. Each option shows both forms, such as /24 (255.255.255.0) or /26 (255.255.255.192), so you can choose whichever you know.
Step 3: Read the network, broadcast, host range and masks
The result cards show the network address, broadcast address, usable host range, subnet mask, wildcard mask, total IPs, usable hosts and IP class. The binary section underneath lines up the mask and address bit by bit, which helps when learning or troubleshooting.
Common Subnet Sizes
- /24 (255.255.255.0): 256 addresses, 254 usable hosts. The typical home or small office LAN.
- /25 (255.255.255.128): 128 addresses, 126 usable hosts.
- /26 (255.255.255.192): 64 addresses, 62 usable hosts.
- /27 (255.255.255.224): 32 addresses, 30 usable hosts.
- /30 (255.255.255.252): 4 addresses, 2 usable hosts, often used for router links.
- /31 and /32: 2-address point-to-point links and single host routes.
How Subnet Calculation Works
An IP subnet calculator online follows the same steps you would do by hand. The subnet mask has 1 bits for the network part and 0 bits for the host part. A bitwise AND of the IP address and the mask gives the network address. Setting all host bits to 1 gives the broadcast address. Every address between them, except those two, can be assigned to a device, which is why a subnet of size 2 to the power n has 2 to the power n minus 2 usable hosts (except /31 and /32).
IP Subnet Calculator Online Tips for Planning Subnets
- Leave room to grow: pick a subnet with at least 30% more addresses than you need today.
- Use private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) for internal networks.
- Avoid overlapping subnets across sites or VPN-connected networks.
- Use the wildcard mask in Cisco ACLs and OSPF network statements.
- Document every subnet with its purpose, VLAN and gateway.
Frequently Asked Questions
Is this IP subnet calculator online free?
Yes. It is free with no sign-up and no limits.
What is CIDR notation?
CIDR writes the subnet mask as the number of network bits after a slash. For example, /24 means the first 24 bits are the network, which equals 255.255.255.0.
How many usable hosts are in a /24?
A /24 has 256 addresses. After removing the network and broadcast addresses, 254 are usable for hosts.
Why does a /31 have 2 usable hosts?
RFC 3021 allows /31 subnets on point-to-point links, where both addresses are used and there is no separate broadcast address.
What is a wildcard mask?
It is the inverse of the subnet mask, for example 0.0.0.255 for a /24. It is used in Cisco access lists and some routing protocols.
Does it support IPv6?
This calculator is for IPv4. IPv6 uses 128-bit addresses and usually /64 subnets for LANs.