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How do I calculate subnets and CIDR ranges online?

Enter an IP address with CIDR notation (e.g., 192.168.1.0/24) to see the network address, broadcast address, usable host range, and total hosts. Use the VLSM divider to split networks, convert IP ranges to CIDR, or classify any IP address. Everything runs in your browser.

Calculate subnet details
Input
IP: 192.168.1.0
CIDR: /24
Output
Network: 192.168.1.0/24
Netmask: 255.255.255.0
Broadcast: 192.168.1.255
Hosts: 254 usable
Range: 192.168.1.1 – .254
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IP / CIDR Toolkit

Subnet calculator, VLSM divider, IP range converter, and IP address classifier — all in one toolkit.

Common Subnets

Network Address
192.168.1.0
Broadcast Address
192.168.1.255
Subnet Mask
255.255.255.0
Wildcard Mask
0.0.0.255
CIDR Notation
192.168.1.0/24
First Usable Host
192.168.1.1
Last Usable Host
192.168.1.254
Total Addresses
256
Usable Hosts
254
IP Class
Class C
Range Type
Private (RFC 1918)
▶CIDR Reference Table
CIDRSubnet MaskAddressesUsable Hosts
/8255.0.0.016,777,21616,777,214
/9255.128.0.08,388,6088,388,606
/10255.192.0.04,194,3044,194,302
/11255.224.0.02,097,1522,097,150
/12255.240.0.01,048,5761,048,574
/13255.248.0.0524,288524,286
/14255.252.0.0262,144262,142
/15255.254.0.0131,072131,070
/16255.255.0.065,53665,534
/17255.255.128.032,76832,766
/18255.255.192.016,38416,382
/19255.255.224.08,1928,190
/20255.255.240.04,0964,094
/21255.255.248.02,0482,046
/22255.255.252.01,0241,022
/23255.255.254.0512510
/24255.255.255.0256254
/25255.255.255.128128126
/26255.255.255.1926462
/27255.255.255.2243230
/28255.255.255.2401614
/29255.255.255.24886
/30255.255.255.25242
/31255.255.255.25422
/32255.255.255.25511

About Subnet Calculation

  • CIDR notation combines an IP address with a prefix length (e.g., 192.168.1.0/24).
  • The prefix length defines how many bits are the network portion — the rest are host bits.
  • Network address = all host bits set to 0. Broadcast = all host bits set to 1.
  • Usable hosts = total addresses minus network and broadcast (except /31 and /32 special cases).
  • Private ranges (RFC 1918): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.
  • Everything runs in your browser — no data is sent over the network.

Tips & Best Practices

Pro Tip

/24 gives 254 usable hosts — the standard small network

A /24 subnet (255.255.255.0) provides 256 addresses with 254 usable for hosts (network and broadcast addresses are reserved). For most office LANs and VPCs, /24 is the right starting point. /16 gives ~65K hosts (large campus), /8 gives ~16M (enterprise backbone). Memorize /24, /16, /8 — derive others from there.

Common Pitfall

Private IP ranges overlap — plan before peering VPCs

RFC 1918 defines 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 as private. When connecting two VPCs or VPNs, overlapping CIDR blocks cause routing conflicts. If both use 10.0.0.0/16, you can't peer them. Plan non-overlapping ranges from day one: 10.1.0.0/16 for production, 10.2.0.0/16 for staging, etc.

Real-World Example

Use /32 for single-host allow rules in security groups

In AWS security groups, GCP firewall rules, or iptables, 203.0.113.5/32 means exactly one IP address. Use /32 for bastion host SSH rules and admin panel access. Common mistake: using /24 or /16 when you meant to restrict to a single IP, accidentally allowing 254 or 65K addresses.

Security Note

IPv6 /128 is the equivalent of IPv4 /32

In IPv6, a /128 prefix identifies a single host. The standard subnet allocation is /64 (18 quintillion addresses per subnet). ISPs typically assign /48 to businesses and /56 to residential customers. Never run IPv6 without a firewall — the myth that NAT provided security in IPv4 does not apply.

Frequently Asked Questions

How do I calculate the number of usable hosts in a subnet?
The formula is 2^(32-prefix) - 2, subtracting the network address and broadcast address. A /24 has 2^8 - 2 = 254 usable hosts. A /30 has 2 usable hosts, ideal for point-to-point links. A /31 is a special case (RFC 3021) with 2 usable addresses and no broadcast. DevBolt's subnet calculator shows host count, network address, broadcast address, and usable range instantly for any CIDR input.
What is CIDR notation and how does it relate to subnet masks?
CIDR notation expresses an IP and subnet mask as 192.168.1.0/24. The number after the slash indicates how many bits are the network portion. /24 = 255.255.255.0, /16 = 255.255.0.0, /8 = 255.0.0.0. CIDR replaced classful addressing (Class A/B/C) for more flexible allocation and smaller routing tables. DevBolt converts between CIDR and dotted-decimal mask notation.
What is VLSM and when should I use it?
VLSM (Variable Length Subnet Masking) divides a network into subnets of different sizes, each with a different prefix. Unlike fixed-length subnetting, VLSM matches subnet sizes to actual host requirements: a department with 100 hosts gets /25 while a point-to-point link gets /30. Sort requirements largest-first, allocate the largest subnet first, then subdivide remaining space. DevBolt's VLSM divider automates this calculation from a list of host count requirements.

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