IPv4 Subnet Calculator

Enter a network in CIDR notation, optionally add a deeper prefix to split it into equal‑sized subnets.

How to use this calculator

  1. 1

    Enter a CIDR block

    Type any valid IPv4 address with a prefix length into the first field — for example 192.168.1.0/24 or 10.0.0.0/8. The address before the slash does not need to be the exact network address; the calculator will derive it automatically.

  2. 2

    Optionally split into subnets (the second field)

    Enter a new prefix length larger than the base prefix to divide the network into equal-sized subnets. For example, entering 28 against a /24 base will produce 16 subnets of /28. Leave this field blank if you only need the base subnet info.

  3. 3

    Read your results

    Click Calculate to see the network address, broadcast address, subnet mask, wildcard mask, usable host range, and total host count. If you used the split field, the full list of subnets appears below in a scrollable panel.

What is IPv4 subnetting?

Subnetting is the process of dividing a single IP network into smaller, logically isolated sub-networks. Each subnet has its own network address, broadcast address, and a range of usable host addresses. Network administrators use subnetting to improve performance by reducing broadcast traffic, enforce security boundaries between departments or services, and allocate IP address space efficiently without waste.

IPv4 addresses are 32-bit numbers written in dotted-decimal notation — four groups of 0–255 separated by dots. A subnet mask (or its shorthand, CIDR prefix notation like /24) defines which bits of the address identify the network and which identify individual hosts. The prefix number is simply a count of the leading network bits: a /24 fixes 24 bits for the network, leaving 8 bits for hosts — giving 256 total addresses and 254 usable ones.

Common use cases include designing corporate LAN segments, configuring cloud VPCs in AWS or Azure, writing firewall ACL rules, setting up home VLANs, and studying for networking certifications like CCNA or CompTIA Network+. Our full subnetting guide covers the topic from first principles if you'd like to dig deeper.

CIDR quick-reference

The most commonly used subnet sizes and their usable host counts.

CIDR Subnet Mask Total Addresses Usable Hosts Wildcard Mask
/16255.255.0.065,53665,5340.0.255.255
/20255.255.240.04,0964,0940.0.15.255
/22255.255.252.01,0241,0220.0.3.255
/24255.255.255.02562540.0.0.255
/25255.255.255.1281281260.0.0.127
/26255.255.255.19264620.0.0.63
/27255.255.255.22432300.0.0.31
/28255.255.255.24016140.0.0.15
/29255.255.255.248860.0.0.7
/30255.255.255.252420.0.0.3
/32255.255.255.25510 (host route)0.0.0.0

Usable hosts = 2(32 − prefix) − 2. A /30 is commonly used for point-to-point router links; a /32 represents a single host route.

📖 Subnetting Guide

Learn how subnetting works from scratch — binary math, CIDR, VLSM, wildcard masks, and common mistakes explained with worked examples.

❓ FAQ

Quick answers to the most common subnetting questions — what /24 means, how to count hosts, private IP ranges, wildcard masks, and more.