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IPv4 Subnet Calculator
PREFIX REFERENCE
Prefix Netmask Addresses
// about this tool

IPv4 Subnet Calculator Online

Updated 2026-08-04

// how to use

  1. 1 Type an address in CIDR form, like 192.168.1.130/26. A plain IP and netmask works too.
  2. 2 Read the network, broadcast and host range off the four cards at the top.
  3. 3 Click any row in the prefix reference to see that subnet size worked out.

// examples

A /26 inside a home network
Input
192.168.1.130/26
Output
Network 192.168.1.128, broadcast 192.168.1.191, hosts .129 to .190, 62 usable
IP and netmask instead of a prefix
Input
172.16.5.1 255.255.0.0
Output
Recognised as /16 — the mask is converted for you
A point-to-point link
Input
203.0.113.7/31
Output
Two usable addresses, no broadcast — RFC 3021, where the usual minus-two does not apply

// common uses

Splitting an office or VPC network into subnets Working out whether two addresses are on the same network Converting between a netmask and a prefix length for a router config Getting the wildcard mask for a Cisco ACL

// faq

Why does a /31 show two usable hosts instead of zero?
Because RFC 3021 allows a /31 on point-to-point links, where both addresses are usable and there is no broadcast. The familiar "total minus two" rule assumes a network and a broadcast address exist, which is not true at /31 or /32. Many calculators report 0 usable hosts here, which would tell you a perfectly valid link config is impossible.
What is the wildcard mask for?
It is the netmask inverted, and it is what Cisco ACLs and OSPF take instead of a netmask. A /24 has a netmask of 255.255.255.0 and a wildcard of 0.0.0.255.
Why show the binary?
Because the mask only really makes sense in binary — you can see exactly where the network part stops and the host part begins. Once you have seen /26 as twenty-six 1 bits followed by six 0 bits, the arithmetic stops being magic.
What counts as a private address?
The RFC 1918 ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), plus loopback, link-local (169.254.x.x) and carrier-grade NAT (100.64.0.0/10). The scope badge names which one you are in, which is usually enough to explain why something is not reachable.
Is anything sent to a server?
No. The calculation happens in your browser, so internal addressing you paste in stays on your machine.

// works with your data

Number Base Converter Hex to Decimal URL Parser User Agent Parser PX to REM Converter

Use this via API

Get a free API key → 
curl -X POST https://thesnaptools.com/api/v1/tools/ipv4-subnet \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"cidr":"192.168.1.130/26"}'
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