Subnet Calculator & Quick-Reference Table — Free, /1–/32 CIDR

Instantly calculate the network address, broadcast address, and usable host count from an IPv4 address and subnet mask. Includes a full /1–/32 subnet mask quick-reference table for network design and troubleshooting — free, no sign-up required.

IP Address (IPv4)
Subnet Mask
Network Address {{ networkAddress }}
Broadcast Address {{ broadcastAddress }}
Number of IP Addresses {{ count }}
Range of Allocatable IP Addresses {{ allocatableStart }} - {{ allocatableEnd }}

CIDR Quick-Reference Table (/1–/32)

Prefix Subnet Mask Total Addresses Usable Hosts
/1 128.0.0.0 2,147,483,648 2,147,483,646
/2 192.0.0.0 1,073,741,824 1,073,741,822
/3 224.0.0.0 536,870,912 536,870,910
/4 240.0.0.0 268,435,456 268,435,454
/5 248.0.0.0 134,217,728 134,217,726
/6 252.0.0.0 67,108,864 67,108,862
/7 254.0.0.0 33,554,432 33,554,430
/8 255.0.0.0 16,777,216 16,777,214
/9 255.128.0.0 8,388,608 8,388,606
/10 255.192.0.0 4,194,304 4,194,302
/11 255.224.0.0 2,097,152 2,097,150
/12 255.240.0.0 1,048,576 1,048,574
/13 255.248.0.0 524,288 524,286
/14 255.252.0.0 262,144 262,142
/15 255.254.0.0 131,072 131,070
/16 255.255.0.0 65,536 65,534
/17 255.255.128.0 32,768 32,766
/18 255.255.192.0 16,384 16,382
/19 255.255.224.0 8,192 8,190
/20 255.255.240.0 4,096 4,094
/21 255.255.248.0 2,048 2,046
/22 255.255.252.0 1,024 1,022
/23 255.255.254.0 512 510
/24 255.255.255.0 256 254
/25 255.255.255.128 128 126
/26 255.255.255.192 64 62
/27 255.255.255.224 32 30
/28 255.255.255.240 16 14
/29 255.255.255.248 8 6
/30 255.255.255.252 4 2
/31 255.255.255.254 2 2
/32 255.255.255.255 1 1

What Is a Subnet Calculator?

An IP address is made up of two parts: a network portion and a host portion. The subnet mask defines exactly where that boundary falls, and the same information can also be written as a prefix length such as /24. This tool only needs an IPv4 address and its mask — enter both, and it instantly works out the network address, the broadcast address, and the range of allocatable addresses along with how many there are.

The usable host count always comes out to "a power of two, minus two" because the first address in a subnet is reserved as the network address and the last as the broadcast address, so neither can be handed out to a device. Further down this page you will also find a full quick-reference table from /1 through /32, letting you compare prefix lengths side by side when planning a network.

How to Use the Subnet Calculator

  1. Enter the IP address Type in any IPv4 address on the network you're working with. It doesn't matter which address within that network you choose — the resulting network address will be the same.
  2. Specify the subnet mask You can enter it either in dotted-decimal form, such as 255.255.255.0, or as a prefix length, such as /24.
  3. Check the calculated results The network address, broadcast address, and the allocatable range with its total count are displayed immediately.
  4. Compare alternatives in the reference table Scan the table to judge which prefix length best fits the number of hosts you actually need, without doing the math by hand.

Tips for getting more out of it

  • /24 (255.255.255.0) is the most common subnet, supporting up to 254 hosts.
  • /32 specifies a single IP address. Used for firewall rules or pinpointing a specific host.
  • Common private IP ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 (RFC 1918).
  • The number of usable hosts is 2(32−prefix length) − 2 (subtracting the network address and broadcast address).

Common Uses for Subnet Calculation

Designing an office or company network

Work out the right prefix length from the number of devices each department needs, leaving enough headroom without wasting addresses.

Sizing a DHCP pool

Once you know the allocatable range, you can carve out a DHCP pool that precisely excludes any addresses reserved for static assignments.

Diagnosing connectivity problems

Calculate the network address for two devices' IPs and masks separately to confirm whether they actually sit on the same network — a mismatched mask is a very common culprit.

Writing firewall rules

Express the exact range you want to allow or block in CIDR notation, avoiding the common mistake of opening up a wider range than intended.

Splitting an address block across VLANs or sites

When dividing a larger address space into multiple VLANs or locations, the calculator immediately shows whether the resulting subnets overlap.

Subnetting Terms Explained

Subnet mask
A value that marks how much of an IP address belongs to the network portion, written as four numbers like 255.255.255.0.
CIDR
A notation that writes the prefix length as a slash followed by a number, such as /24. It expresses the same information as a subnet mask, only more compactly.
Network address
The first address in a subnet. It identifies the network itself rather than any single device, so it is never assigned to a host.
Broadcast address
An address used to send data to every device on a subnet at once. It sits at the end of the range and, like the network address, is never assigned to a host.
Private IP address
An address from a range reserved for use inside an organization only. These addresses are never routed directly onto the public internet.
NAT
Network Address Translation — a mechanism that converts private IP addresses to a public one and back, letting many devices share a single external address.
Subnetting
The practice of splitting a larger network into smaller subnets, which makes management easier and keeps broadcast traffic contained to a sensible scope.
VLSM
Variable Length Subnet Masking — using subnet masks of different sizes within the same network to allocate addresses more efficiently instead of wasting them on a one-size-fits-all mask.

FAQ

The first address in a subnet is reserved as the network address and the last as the broadcast address; neither can be assigned to a host, so two addresses are always subtracted.

/31 (RFC 3021) is used for point-to-point links between routers. /32 identifies a single host and is commonly used in firewall rules or static routing entries.

CIDR notation (e.g. /24) expresses the prefix length as a slash followed by a number, while a subnet mask (e.g. 255.255.255.0) represents the same information as a 32-bit value — they are two ways of describing the same thing.
Tool-kun

Side Note — The IPv4 Exhaustion Problem: The Day 4.3 Billion Addresses Ran Out

IPv4 addresses are 32 bits, providing approximately 4.3 billion addresses. However, the rapid growth of the internet led to IANA (the Internet Assigned Numbers Authority) fully exhausting its pool in February 2011. APNIC, which manages the Asia-Pacific region, also depleted its standard allocation in April of the same year. The transition to IPv6 (128 bits, approximately 3.4×1038 addresses) is now well underway.

The technology that served as a stopgap for IPv4 exhaustion is NAT (Network Address Translation). Home and office routers allow many devices with private IP addresses to share a single global IP, keeping IPv4 viable today. The private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are defined by RFC 1918 and are not directly routed on the internet.

As of 2024, IPv6 adoption rates have reached around 40–50% globally. Meanwhile, dual-stack operation — running IPv4 and IPv6 side by side — continues, and development of interoperability and migration tools remains active.

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