IP Subnet & CIDR Calculator
Work out network, broadcast, masks and host ranges for IPv4 and IPv6, plan VLSM, aggregate routes and check overlaps. Everything runs in your browser.
- IPv4 and IPv6
- VLSM and supernet
- Free, no account
Network: 192.168.1.0 Broadcast: 192.168.1.255 Mask: 255.255.255.0 Hosts: 192.168.1.1 - .254 Usable: 254
IPv4 address
Results update as you type.
Nothing calculated yetEnter an IPv4 address and a prefix.
Binary breakdown click a host bit to flip it
network bits host bits
Split into smaller subnets
IPv6 address
Nothing calculated yetEnter an IPv6 address and a prefix length.
VLSM planner
The largest subnet is placed first so all blocks stay aligned.
Nothing planned yetAdd a base network and at least one host count.
Reverse lookup
Finds the smallest CIDR block that contains both addresses.
Nothing calculated yetEnter two IPv4 addresses.
Supernet
Finds the smallest single block that covers every network listed.
Nothing calculated yetAdd one or more CIDR blocks.
IP in range
Nothing checked yetEnter an IP address and a network.
Overlap check
Nothing checked yetEnter two networks.
Minimum CIDR
Finds the smallest subnet that fits that many usable hosts.
Nothing calculated yetEnter how many hosts you need.
CIDR reference
Every prefix from /0 to /32 with its mask, wildcard and host count.
No matchNo prefix matches that filter.
Subnetting practice
0 / 0Random multiple-choice questions. Your score and best streak are saved in this browser.
Saved calculations
Use Save to history on the IPv4 tab. Entries stay in this browser only and are not shared between devices.
How It Works
-
1
Pick a Calculator
Choose IPv4 or IPv6 for a full breakdown, or one of the planning tools such as VLSM, Supernet or Overlap Check.
-
2
Enter the Network
Type an address and a prefix or mask. You can also paste ip/cidr in one go. Results update as you type.
-
3
Copy or Export
Copy any value, copy a summary, download the host list as CSV, or share a link to the exact calculation.
Subnetting Basics
CIDR and masks
A prefix like /24 means the first 24 bits are the network and the rest are hosts. /24 is the same as the mask 255.255.255.0, and you can type either one.
Usable hosts
A subnet loses two addresses to the network and broadcast address, so /24 gives 254 usable hosts. /31 (point-to-point) and /32 (single host) are special cases.
VLSM
Variable length subnet masking sizes each subnet to its need. The planner places the largest subnet first so every block stays aligned and nothing overlaps.
Supernetting
Aggregation replaces several routes with one shorter prefix. It is exact only when the networks are adjacent and fill the whole block, otherwise it also covers unused space.
Calculations follow standard IPv4 and IPv6 rules. Always double-check addressing plans before applying them to production equipment. Nothing you type is sent anywhere.
Frequently asked questions
What is CIDR notation?
It writes an IP range as an address and a prefix length, for example 192.168.1.0/24, where /24 means the first 24 bits identify the network.
How many usable hosts are in a /24?
254. A /24 has 256 addresses, and two are kept for the network address and the broadcast address.
What is VLSM?
Variable Length Subnet Masking splits one network into subnets of different sizes, so each subnet gets only the addresses it needs.
What is supernetting?
It combines neighbouring networks into one larger prefix, also called route aggregation or summarisation, which keeps routing tables shorter.
Does it support IPv6?
Yes. It shows the IPv6 network prefix and address range as well as the IPv4 network, broadcast, mask and host range.
Are my calculations saved or sent anywhere?
The calculator runs in your browser. If you use Save to history, entries stay in this browser only and are not shared between devices.
Need a custom tool?
Tell us the task and we can build a dedicated tool for you, with its own capacity.