This IP subnet calculator returns the IPv4 network address for an IP and CIDR prefix. Enter a dotted quad and a prefix length to see the network in address/prefix form.
Network students and admins use it to confirm which subnet an interface address belongs to before writing routes or firewall rules. It focuses on the network ID, not a full inventory of every host.
How the network ID is found
The tool converts the IP to a 32 bit number, builds a mask from the CIDR length, bitwise ANDs them, converts back to dotted decimal, and appends /cidr.
Worked example
IP 192.168.1.10, CIDR 24. Network result is 192.168.1.0/24.
| Input | Value |
|---|---|
| IPv4 address | 192.168.1.10 |
| CIDR prefix | 24 |
| Network | 192.168.1.0/24 |
How to use the fields
- IPv4 address must have four octets from 0 to 255.
- CIDR prefix is an integer from 1 to 32.
- Use the prefix that matches the interface mask you were given.
Reading CIDR quickly
/24 keeps the first three octets as the network and leaves 8 host bits. /16 keeps the first two octets. /32 is a single host route. Smaller prefixes mean larger networks and more host addresses.
Common mistakes
- Mixing decimal masks like 255.255.255.0 with the wrong CIDR
- Typing commas or spaces inside the IP
- Assuming the calculator lists usable hosts when it returns only the network ID
- Applying IPv4 habits to IPv6 addressing without a different tool
Lab and ops tips
When two devices cannot ping, confirm they share the same network ID and that the gateway sits in that subnet. If VPN and LAN ranges overlap, recalculate both sides so you can spot collisions before users complain.
Document the network ID beside the interface IP in change tickets. That habit prevents accidental /16 style mistakes when someone meant /24.
CIDR size intuition
Each step down in prefix length roughly doubles the address space. Moving from /24 to /23 doubles hosts; moving from /24 to /25 halves them. Plan capacity from required hosts plus room for growth, then pick a prefix, then verify the network ID with this calculator on a sample address.
Overlapping subnets cause hard to debug routing problems. Before you add a new VLAN or VPN pool, compute network IDs for both sides and confirm they do not collide.
Checklist for interface changes
- Write the intended CIDR beside the host IP before you edit the interface.
- Confirm the gateway sits inside the same network ID.
- Update DNS, DHCP scopes, and firewall objects that still reference the old prefix.
- Ping the gateway and a remote test host after the change.
A thirty second network ID check here often saves an hour of downtime later.
Private ranges quick map
Common private blocks include 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Home routers often use 192.168.0.0/24 or 192.168.1.0/24. Enter any host in the LAN and /24 to confirm the network ID matches what the router LAN page shows.
When you build a lab with multiple virtual networks, allocate non overlapping prefixes first, then verify each gateway address lands in its own network ID. This calculator makes that verification fast during setup.
Mask length examples
A /30 is often used on point to point links with only a few addresses. A /29 or /28 may fit a small DMZ. A /24 remains the everyday LAN size in many offices and homes. Enter a host in each of those prefixes once so you build intuition for how the network ID changes when host bits shrink.
Document the chosen prefix in the same ticket as the gateway and DHCP pool. Future you will thank present you when a VPN route needs an update.
If two sites both use 192.168.1.0/24, one side must renumber or you will fight asymmetric routing forever. Catch that collision at planning time with this network ID check.
Print or paste the resulting network string into your runbook beside DHCP start and end addresses so operators see one consistent picture.
Limitations
Results do not enumerate host ranges, broadcast addresses, or wildcard masks. They also do not validate whether an address is public or private beyond basic IPv4 parsing. Use them as a fast network ID check beside your fuller IP plan.
For related unit and percent checks while you plan materials, try the unit converter or the percentage calculator.