IPv4 Subnet Calculator
CIDR, masks, ranges and subnet splitting with a visual map of the address space.
100% in your browser. Nothing you type ever leaves this page.
- Netmask
- 255.255.255.0
- Wildcard
- 0.0.0.255
- Mask (hex)
- 0xFFFFFF00
- Broadcast
- 192.168.1.255
- Total addresses
- 256
- First host
- 192.168.1.1
- Last host
- 192.168.1.254
- PTR zone
- 1.168.192.in-addr.arpa
- IP (binary)
- 11000000.10101000.00000001.00000000
- Integer
- 3232235776
Split this network
| # | Subnet | Usable range | Broadcast | Hosts |
|---|
Self-test passed: 6 reference subnets verified on load.
Reading the results like a network engineer
The two numbers that matter in daily work are the network address and the usable range. The network address (host bits all zero) is what you put in routing tables and firewall rules. The usable range is what you can actually assign: DHCP scopes, server IPs, printer reservations. The broadcast address (host bits all one) is taken, and so is the network address itself, which is why a /24 gives you 254 hosts, not 256. If you want the bit-level story, our guide What is a /24? takes it apart with diagrams.
The prefix slider is the fastest way to plan
Drag the prefix and watch the usable host count: that is capacity planning in one gesture. Need 500 devices on one VLAN? A /24 is too small and a /23 (510 usable) barely fits, so take a /22 and breathe. Building a point-to-point link between two routers? A /30 wastes two addresses; modern gear happily runs /31 per RFC 3021 and this calculator handles that case correctly, including the missing broadcast address.
Special ranges the tool flags for you
Paste any address and the scope badge tells you what you are looking at: RFC 1918 private space, loopback, link-local (the 169.254 addresses that appear when DHCP fails), carrier grade NAT space (100.64/10, common behind 4G/5G), documentation prefixes, multicast or plain public space. It reads the IANA special-purpose registry so you do not have to memorize it. The classful A/B/C labels are also shown because exam questions and old documentation still use them, but routing has been classless since 1993: the prefix length is the only thing that counts.
Splitting without spreadsheet pain
The splitter answers the question every junior admin asks with a spreadsheet and every senior admin asks with this kind of tool: "if I cut this /22 into /26es, what exactly do I get?" Click a target prefix and read the table: each child subnet with its range and broadcast, ready to paste into your IPAM or a ticket. The CSV export exists because network documentation lives in spreadsheets whether we like it or not.
Frequently asked questions
Why does a /24 have 254 usable hosts and not 256?
A /24 contains 256 addresses, but the first one identifies the network itself and the last one is the broadcast address. Routers and hosts will not accept them as interface addresses, which leaves 254 for actual devices. The exceptions are /31 (both addresses usable on point-to-point links, RFC 3021) and /32 (a single host route).
What is the difference between a subnet mask and a wildcard mask?
They are bitwise inverses of each other. The subnet mask 255.255.255.0 corresponds to the wildcard 0.0.0.255. Subnet masks describe networks on interfaces; wildcard masks show up in Cisco ACLs and OSPF network statements, where a 0 bit means "must match" and a 1 bit means "anything goes".
How do I know if an IP address is private?
Three blocks are reserved for private use by RFC 1918: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. This calculator flags them automatically, along with loopback (127/8), link-local (169.254/16), carrier-grade NAT (100.64/10) and other special-purpose ranges from the IANA registry.
Can I split a network into subnets of different sizes?
Yes, that is VLSM (variable length subnet masking), and it is how real networks are carved up. This tool splits a block into equal child subnets to keep the table readable; for mixed sizes, split once, then run the calculator again on one of the children with a longer prefix.
Does this calculator work offline?
Yes. The math is plain JavaScript running in your page. Once the page has loaded you can disconnect from the network and keep calculating; nothing is sent to any server.