Subnet Calculator: IPv4 & IPv6 CIDR, Mask & Hosts
Type an IPv4 or IPv6 CIDR and see the range, mask and usable hosts as you type. Drag the prefix, size a subnet for AWS, Azure or Google Cloud and split large blocks without sending your plan to a server.
- Live results with a draggable prefix bar
- Usable hosts for AWS, Azure and Google Cloud
- Exact IPv6, subnet splitting and a cheat sheet
Ready. Inputs are not added to the URL or analytics.
IPv4 /31 has two endpoints for a point-to-point link; /32 is one address. IPv6 has no broadcast. Counts describe address space, not a guarantee that every address is assignable or reachable.
Size a subnet for your hosts
Standard IPv4 networks lose the network and broadcast address. AWS and Azure reserve 5 addresses per subnet and Google Cloud reserves 4. Check your provider’s current limits before you deploy.
The link carries the network you entered after the # sign. Share it only when that is fine.
Split into smaller subnets
| Network / CIDR | First address | Last address |
|---|
Private reports
Reports hide addresses and names by default. Enable the option only when you want to include them. Files and printing are generated locally; no share URL or saved history is created.
How to use this tool
- Type an address with a prefix, such as 192.168.1.10/24 or 2001:db8::/48. Results update as you type.
- Drag the prefix bar, or enter the hosts you need and your platform to get the right size.
- Split the range into smaller subnets, copy a link to the calculation or export a report.
Read the result
CIDR separates the network bits from the host bits. The calculator clears the host bits to find the network and sets them to find the last address. IPv4 broadcast and traditional host ranges are separate from the full address range. IPv6 has no broadcast address. Exact integer arithmetic keeps large IPv6 counts precise. These are mathematical results, not allocation records, routing evidence or a scan of your network.
Subnet cheat sheet: masks and host counts
| Prefix | Subnet mask | Addresses | Usable hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /12 | 255.240.0.0 | 1,048,576 | 1,048,574 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 512 | 510 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 |
| /32 | 255.255.255.255 | 1 | 1 |
Common IPv6 prefixes
| Prefix | /64 subnets inside |
|---|---|
| /32 | 4,294,967,296 |
| /40 | 16,777,216 |
| /48 | 65,536 |
| /56 | 256 |
| /60 | 16 |
| /64 | 1 |
Questions and answers
How many usable hosts are in a /24, /26 or /28?
On a standard network a /24 has 256 addresses and 254 usable hosts, a /26 has 62 and a /28 has 14. Cloud platforms keep more: an AWS or Azure /28 leaves 11 and a Google Cloud /28 leaves 12. The cheat sheet lists every common prefix.
Can I enter a subnet mask instead of /24?
Yes. Enter an IPv4 address followed by a space or slash and a contiguous dotted mask, such as 192.168.1.10 255.255.255.0. Masks with gaps are rejected.
Why are /31 and /32 different?
A /31 can use both endpoints on a point-to-point IPv4 link under RFC 3021. A /32 names one address. The traditional subtract-two host rule does not apply to these cases.
Will splitting a large IPv6 block freeze my browser?
The tool shows at most 32 child subnets per page and reports the exact total. It never expands every host or silently truncates the total to the displayed rows.