Tools
Subnet Calculator for IPv4 and IPv6
Type an address with its prefix, such as 192.168.10.0/26 or 2001:db8::/48, and get the network, broadcast, usable range and host count at once. The maths runs in your browser; nothing is sent to us.
IPv4. Private (RFC 1918). Class C.
- Network
- 192.168.10.0/24
- Broadcast
- 192.168.10.255
- First Host
- 192.168.10.1
- Last Host
- 192.168.10.254
- Subnet Mask
- 255.255.255.0
- Wildcard
- 0.0.0.255
- Total Addresses
- 256
- Usable Hosts
- 254
- Binary Mask
- 11111111.11111111.11111111.00000000
How to Read the Results
- Network
- The first address of the block. It names the subnet and is not given to a host.
- Broadcast
- The last address of an IPv4 block, used to reach every host on it. IPv6 has no broadcast.
- First and Last Host
- The range you can give to devices. For /31 and /32 every address is usable.
- Mask and Wildcard
- The mask in dotted form, and its inverse, which Cisco ACLs and OSPF statements use.
Worked Example: Splitting a /24 Into Four
A /24 holds 256 addresses. Borrow two bits and you get four /26 subnets of 64 addresses, each with 62 usable hosts:
| Subnet | Hosts | Broadcast |
|---|---|---|
192.168.10.0/26 | .1 to .62 | .63 |
192.168.10.64/26 | .65 to .126 | .127 |
192.168.10.128/26 | .129 to .190 | .191 |
192.168.10.192/26 | .193 to .254 | .255 |
IPv6 Is Different
In IPv6 you do not size subnets to fit hosts: a LAN is a /64, and point to point links are usually /127. The calculator shows the first and last address and the total, and notes when a prefix will not work with SLAAC. The IPv6 design guide explains why.
Questions People Ask
Why Does a /31 Have Two Usable Hosts?
RFC 3021 allows /31 on point to point links, where a network and broadcast address would waste half the block. Both addresses go to the two ends of the link.
Why Does It Refuse 256.1.1.1 or 010.0.0.1?
Each IPv4 part runs from 0 to 255, and leading zeros are read as octal by some systems, so we refuse them rather than guess.
Is My Input Sent Anywhere?
No. Everything is worked out in your browser.
Which Ranges Are Private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918). The calculator also names loopback, link local, carrier grade NAT, documentation and multicast ranges.
Practise It
Try the subnetting questions in the networking quiz, or turn a list of subnets into summary routes with the route summariser.
Carving one block into subnets of different sizes? The VLSM planner lays them out largest first and shows what is left.
Planning an addressing scheme for real? See our network and identity design work, or send us the brief.