What's the difference between a subnet mask and CIDR notation?
Same information, different format — 255.255.255.0 and /24 both mean 24 network bits; CIDR is just shorthand.
IPv4 Subnet Calculator
CIDR block
VLSM split
/24 · Class C256 addresses
Subnet details
- Network
- 192.168.1.0
- Broadcast
- 192.168.1.255
- Host range
- 192.168.1.1 – 192.168.1.254
- Subnet mask
- 255.255.255.0
- Wildcard mask
- 0.0.0.255
- Total addresses
- 256
- Usable hosts
- 254
- IP class
- C
- IP scope
- Private (RFC 1918)
Bit visualization
NetworkHost
IP address
11000000
10101000
00000001
00000000
Subnet mask
11111111
11111111
11111111
00000000
Network address
11000000
10101000
00000001
00000000
About this IPv4 Subnet Calculator
Calculate the network address, broadcast address, host range, and subnet/wildcard masks for a CIDR block, and split it into a VLSM table by subnet count or host requirements.
Everything is computed locally in your browser. Subnetting splits one large network into smaller, right-sized segments — cutting broadcast traffic and avoiding wasted address space. Enter a CIDR block such as 192.168.1.0/24 (or an IP address and prefix separately) to see its subnet details, a bit-level view of where the prefix boundary falls, and whether it's a private or public range, then optionally split it into a VLSM table by subnet count or host requirements.
For example, splitting 192.168.1.0/24 by host counts 50, 20, and 10 assigns a /26 (64 addresses) to the 50-host subnet, a /27 (32 addresses) to the 20-host one, and a /28 (16 addresses) to the smallest — each sized to just fit its requirement instead of handing every subnet an identical block.
FAQ
How do I calculate usable hosts in a subnet?
2^(32 − prefix length) − 2, minus the network and broadcast addresses (special rules apply for /31 and /32).
Why can't the network and broadcast addresses be assigned to a device?
The network address (all host bits 0) identifies the subnet itself, and the broadcast address (all host bits 1) reaches every host on it — neither one identifies a single device. Both are reserved automatically, except on /31 point-to-point links and /32 host routes, which have none to reserve.
Why does a /24 only give 254 usable addresses?
A /24 has 256 total addresses (2^8), but the first is the network address and the last is the broadcast address — both reserved, leaving 256 − 2 = 254 for devices (see the question above). The same −2 rule applies to any prefix shorter than /31.
What are the reserved private IPv4 ranges?
10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 (RFC 1918), plus 169.254.0.0/16 for link-local.
How is an IP address determined to be private vs. public?
Private addresses fall inside one of the three RFC 1918 ranges reserved for internal networks (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). This tool checks the network address against those three blocks automatically and shows the result as "IP scope" — anything outside them is public and routable on the internet.
Does this support splitting a network into multiple subnets (VLSM)?
Yes, in two modes: Equal subnets splits the parent network into N equal-sized blocks, while By host count (classic VLSM) sizes each subnet automatically to fit the host counts you enter, packing differently-sized subnets from one base network in a single pass.
What's a wildcard mask?
The inverse of a subnet mask, used in ACLs/OSPF — where a subnet mask has 1s for network bits, a wildcard mask has 0s.
Are IP classes (A/B/C) still relevant?
Not for sizing a network — 1990s classful addressing gave every network a fixed size (Class A ≈16.7M addresses, B ≈65k, C 256), which wasted huge blocks of address space and was replaced by CIDR's variable-length prefixes. The class shown here is just a legacy label from the first octet; a 192.168.x.x ("Class C") range works fine as a /28 instead of the classful /24 — the actual size is whatever prefix you choose.
Is my IP sent anywhere?
No, entirely client-side.
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