How to use this IP subnet calculator
Type an address with its prefix or mask, like 192.168.1.10/24, 10.0.0.5 255.255.252.0 or 2001:db8::/48. Results update as you type, and the slider changes the prefix length so you can see how the network grows or shrinks. This IP subnet calculator runs entirely in your browser, so nothing you enter is sent anywhere.
The other tabs handle the jobs that come up when you plan a real network:
- Split divides a network into equal subnets, by count, by hosts per subnet or by prefix length, with a CSV download.
- VLAN planner takes a list like “Staff 40, Guest Wi-Fi 30, Cameras 16” and carves right-sized subnets out of one block, with gateways and DHCP ranges.
- Range → CIDR turns a start and end address into the fewest CIDR blocks, which is handy for firewall rules and allow lists.
- IP in subnet? tells you whether an address falls inside a network.
Subnet mask vs. CIDR prefix
A subnet mask and a CIDR prefix say the same thing two ways. The prefix counts how many bits at the start of the address identify the network; the mask writes those bits out as four numbers. A /24 and 255.255.255.0 are identical.
| CIDR | Subnet mask | Usable hosts | Typical use |
|---|---|---|---|
| /30 | 255.255.255.252 | 2 | Link between two routers |
| /29 | 255.255.255.248 | 6 | Small block of public IPs from your provider |
| /28 | 255.255.255.240 | 14 | Network management, a few servers |
| /27 | 255.255.255.224 | 30 | Printers, a small VLAN |
| /26 | 255.255.255.192 | 62 | Phones, cameras |
| /25 | 255.255.255.128 | 126 | A department |
| /24 | 255.255.255.0 | 254 | The classic office or home network |
| /23 | 255.255.254.0 | 510 | A larger office or guest Wi-Fi |
| /22 | 255.255.252.0 | 1,022 | A block to split into VLANs |
Each network loses two addresses: the first is the network address and the last is the broadcast address. The exceptions are /31, used for point-to-point links, and /32, a single host.
Private IP address ranges
These IPv4 ranges are reserved for use inside your own network and are never routed on the internet. Your router or firewall translates them (NAT) when devices go online.
| Range | Addresses | Notes |
|---|---|---|
| 10.0.0.0/8 | 10.0.0.0 – 10.255.255.255 | The largest private block. Great for offices with several VLANs. |
| 172.16.0.0/12 | 172.16.0.0 – 172.31.255.255 | Only 172.16 through 172.31. 172.32.x.x and up are public. |
| 192.168.0.0/16 | 192.168.0.0 – 192.168.255.255 | The usual home and small-office range. |
| 100.64.0.0/10 | 100.64.0.0 – 100.127.255.255 | Carrier-grade NAT used by internet providers. Not for your LAN. |
| 169.254.0.0/16 | 169.254.0.0 – 169.254.255.255 | Self-assigned when a device can’t reach DHCP. |
In IPv6, the private equivalent is the unique local range fc00::/7. In practice you pick a random /48 inside fd00::/8.
IPv6 subnetting in plain English
IPv6 subnetting is simpler than it looks. Your internet provider usually gives you a /48 or a /56. Each network (each LAN or VLAN) gets a /64, which is the size automatic addressing (SLAAC) expects. A /56 holds 256 of those /64 networks and a /48 holds 65,536, so running out isn’t a concern. The calculator shows how many /64s fit in any prefix you enter.
Planning VLANs for a small office
A flat network, where every computer, camera, phone and guest shares one subnet, is common in small offices. Splitting it into VLANs keeps guests away from your files, keeps cameras and smart devices away from your computers, and makes problems easier to trace. A few habits help:
- Give staff, guest Wi-Fi, phones, cameras and printers their own networks, with firewall rules between them.
- Avoid 192.168.0.x and 192.168.1.x for an office. Most home routers use them, which causes conflicts for staff on VPN. A block like 10.20.0.0/22 is a safer start.
- Leave room to grow, and write down every subnet, VLAN ID and gateway. The VLAN planner’s CSV is a good start for that document.
Planning an office network or cleaning up a flat one?
Frequently asked questions
What’s the difference between a subnet mask and CIDR notation?
Nothing but the format. CIDR notation (like /24) counts the network bits; a subnet mask (like 255.255.255.0) writes the same bits out as four numbers. The calculator shows both side by side.
How many usable hosts are in a /24?
254. A /24 has 256 addresses, minus the network address (.0) and the broadcast address (.255).
Is 172.32.0.0 a private IP address?
No. The private block is 172.16.0.0/12, which covers 172.16.0.0 through 172.31.255.255 only. Addresses from 172.32.0.0 upward are public.
What is a wildcard mask?
The inverse of the subnet mask: 0 bits must match and 1 bits can be anything. For a /24 it’s 0.0.0.255. Cisco access lists and OSPF use wildcard masks.
What does a 169.254 address mean?
The device gave itself an address because it couldn’t reach a DHCP server. Check the cable or Wi-Fi connection, the switch port’s VLAN, and whether the DHCP server or scope is full.
What size IPv6 subnet should I use?
Use a /64 for each LAN or VLAN. Providers usually assign a business a /48 or a /56, which you split into /64 networks. Smaller prefixes like /127 are for point-to-point links.
Does this calculator send my IP addresses anywhere?
No. All the math happens in your browser. Nothing you type is sent to or stored by sohologics.com/.
