CIDR Subnet Calculator

Calculate IPv4 subnet ranges, netmasks, wildcard masks, usable hosts, and binary network boundaries locally in your browser.

Browser-BasedResponsive UIPrivacy-First

IP and Prefix Setup

CIDR input

Paste a full IPv4 CIDR value such as 10.0.4.18/20 or 192.168.1.18/24.

IPv4 address

CIDR prefix

Network mask length/24

Slide between /0 and /32 to move the network and host boundary live.

Standard IPv4 mode:The usable count follows traditional IPv4 subnet math, with /31 and /32 handled separately.

Subnet Split Planner

Equal child subnets

Useful for VLAN, VPC, and environment segmentation planning.

Split the current parent network into equal child blocks.

Network summary

192.168.1.0/24

Private Class C network with 254 standard usable addresses.

PrivateClass CStandard IPv4

Calculated Network Details

Entered IP

192.168.1.18

Exact host address you entered.

CIDR Block

192.168.1.0/24

Normalized network block for the address and prefix.

Netmask

255.255.255.0

Dotted decimal subnet mask.

Wildcard Mask

0.0.0.255

Inverse of the subnet mask, often used in ACLs.

Network Address

192.168.1.0

The first address that identifies the subnet itself.

Broadcast Address

192.168.1.255

The highest address in the block.

First Usable Host

192.168.1.1

First host address in standard subnet math.

Last Usable Host

192.168.1.254

Last host address before broadcast.

Total Addresses

256

Every address inside the IPv4 block.

Standard Usable

254

Usable host count with traditional IPv4 rules.

AWS Usable Estimate

251

Planning estimate after five reserved addresses.

Address Scope

Private

Quick hint for RFC 1918 and special ranges.

Class Hint

Class C

Legacy IPv4 class style reference.

Network Bits

Leading bits reserved for the network.

Host Bits

Bits left over for host addressing.

Interactive Bit Grid

The first 24 bits are network bits. Click any bit to toggle the IPv4 address.

Network bitHost bitBit set to 1

IP11000000.10101000.00000001.00010010

Mask11111111.11111111.11111111.00000000

How it works

How this CIDR subnet calculator works

Enter any IPv4 address with a CIDR prefix like 192.168.1.18/24 and instantly see the enclosing network block, netmask, wildcard mask, broadcast address, first and last usable hosts, total addresses, and usable host count. Click the 32-bit grid to flip binary bits and watch the network boundary move in real time.

Switch between standard IPv4 math and AWS mode to compare usable address counts — AWS reserves five addresses per subnet while standard subnetting reserves two. Use the subnet split planner to break a parent block into equal child networks for VPC, VLAN, or office segmentation. All calculations run locally in your browser with zero data uploads.

FAQ

Common Questions

What is CIDR notation?

CIDR stands for Classless Inter-Domain Routing. A value such as 192.168.1.0/24 combines an IPv4 address with a prefix length that tells you how many leading bits belong to the network portion.

How many usable hosts are in a /24 subnet?

A /24 has 256 total IPv4 addresses. In standard subnet math, 254 are usable because one address is the network address and one is the broadcast address.

Why are /31 and /32 subnets different?

A /31 leaves only two addresses and is often treated as a point-to-point pair. A /32 represents a single host route, so the one address is the route target itself.

What is the difference between total and usable addresses?

Total addresses is every IPv4 address inside the block. Usable addresses removes reserved addresses such as the network and broadcast values in traditional IPv4 subnetting.

Why is my entered IP different from the network address shown?

The entered IP can be any host inside the subnet. The calculator normalizes that host to the enclosing network block and shows the network address that the prefix actually defines.

Does AWS use the same usable host count as standard subnet math?

Not exactly. Standard math removes the network and broadcast addresses for most subnets. AWS planning often reserves five IPv4 addresses per subnet, so the AWS mode shows that estimate separately from standard IPv4 math.