IP Subnet Calculator – CIDR, Subnet Mask & Host Range
Free online IP subnet calculator. Calculate CIDR notation, subnet masks, network addresses, broadcast ranges, usable hosts, and wildcard masks instantly.
IP Subnet Calculator
Calculate subnet masks, CIDR ranges, network addresses, broadcast targets, and usable hosts.
Network Information
Host Information
Subnet & Bit Allocation
32-Bit Binary Bit Representation
Interactive Subnet Splitter
Split parent network 192.168.1.0/24 into smaller child subnets.
| Subnet # | CIDR Block | Network Address | Usable Host Range | Broadcast IP | Usable Hosts |
|---|---|---|---|---|---|
| #1 | 192.168.1.0/25 | 192.168.1.0 | 192.168.1.1 – 192.168.1.126 | 192.168.1.127 | 126 |
| #2 | 192.168.1.128/25 | 192.168.1.128 | 192.168.1.129 – 192.168.1.254 | 192.168.1.255 | 126 |
How to Use
IP Subnet Calculator & CIDR Notation Tool
The ToolMono IP Subnet Calculator is a browser-native developer utility designed for network engineers, DevOps specialists, system administrators, and cloud architects. Calculate CIDR slash notation (e.g. /24), dotted-decimal subnet masks (e.g. 255.255.255.0), network and broadcast IP addresses, usable host ranges, and 32-bit binary network/host bit maps instantly.
The tool supports dual input modes (CIDR slash notation vs IP + Subnet Mask dropdown), RFC 1918 private IP classification, RFC 3021 /31 point-to-point boundary handling, /32 host routes, an IP Range-to-CIDR converter, an interactive Subnet Splitter, and a complete /1 to /32 reference table.
Toggle between CIDR notation (e.g. 192.168.1.0/24) and IP + Subnet Mask dropdowns with 2-way automatic synchronization.
All 32-bit binary math, classification lookups, and subnet splits execute 100% locally in your browser with zero remote server logging.
Convert Start and End IP addresses into minimal CIDR blocks, or split parent subnets into smaller child networks with live export options.
How to Calculate an IP Subnet
- Choose Input Mode: Toggle between CIDR Notation (e.g.
192.168.1.0/24) or IP + Subnet Mask (e.g. IP:192.168.1.0, Mask:255.255.255.0). - Review Grouped Results: Inspect Network Information (Network Address, Broadcast Address, Wildcard Mask), Host Information (First/Last Usable IP, Total/Usable Hosts), and Subnet Information.
- Inspect IP Classification & Binary Map: Check the IP classification badge (Private RFC 1918, Public, Loopback) and visual 32-bit binary network (1s) vs host (0s) bit distribution.
- Use Secondary Tools: Switch tabs to IP Range → CIDR to calculate minimal CIDR blocks for an IP span, or use the Subnet Splitter to divide networks into equal subnets.
- Copy or Export: Click Copy JSON, Copy Markdown, Copy Plain Text, or Copy CSV to export results.
IP Range to CIDR & Interactive Subnet Splitter
ToolMono includes two integrated sub-tools for complex network design:
IP Range → CIDR Converter
Enter an arbitrary Start IP (e.g. 192.168.1.0) and End IP (e.g. 192.168.1.255). The engine computes the minimal set of valid CIDR blocks required to cover the IP range without overlapping outside boundaries.
Interactive Subnet Splitter
Select a parent network (e.g. 10.0.0.0/24) and choose a child prefix length (e.g. /26). The splitter generates a full table of child subnets with network addresses, host ranges, and broadcast IPs.
CIDR Notation & Subnet Masks
Classless Inter-Domain Routing (CIDR) replaced legacy Class A, B, and C network addressing in 1993 (RFC 1519). A CIDR prefix length (e.g. /24) denotes the number of leading 1 bits in the 32-bit subnet mask.
RFC 1918 Private IPv4 Address Ranges
RFC 1918 defines three private IPv4 address blocks reserved for internal enterprise LANs, home Wi-Fi networks, and cloud VPC subnets. These addresses are non-routable on the public Internet:
| Class | CIDR Block | IP Address Range | Total IPs |
|---|---|---|---|
| Class A | 10.0.0.0/8 | 10.0.0.0 – 10.255.255.255 | 16,777,216 |
| Class B | 172.16.0.0/12 | 172.16.0.0 – 172.31.255.255 | 1,048,576 |
| Class C | 192.168.0.0/16 | 192.168.0.0 – 192.168.255.255 | 65,536 |
RFC 3021 /31 & /32 Special Cases
/31 Point-to-Point Links (RFC 3021)
Standard subnet math subtracts 2 IPs for network and broadcast addresses. RFC 3021 allows /31 subnets (2 total IPs) on point-to-point router links, making both IP addresses usable host endpoints.
/32 Host Routes
A /32 prefix length represents a single IP address route with subnet mask 255.255.255.255. There are 1 total IP and 1 usable host.
Complete /1 to /32 Subnet Reference Table
Below is the complete reference table for IPv4 prefixes /1 through /32, calculated directly by ToolMono's calculation engine:
| Prefix | Subnet Mask | Wildcard Mask | Total IPs | Usable Hosts | Class / Usage |
|---|---|---|---|---|---|
| /1 | 128.0.0.0 | 127.255.255.255 | 2,147,483,648 | 2,147,483,646 | Class A Range |
| /2 | 192.0.0.0 | 63.255.255.255 | 1,073,741,824 | 1,073,741,822 | Class A Range |
| /3 | 224.0.0.0 | 31.255.255.255 | 536,870,912 | 536,870,910 | Class A Range |
| /4 | 240.0.0.0 | 15.255.255.255 | 268,435,456 | 268,435,454 | Class A Range |
| /5 | 248.0.0.0 | 7.255.255.255 | 134,217,728 | 134,217,726 | Class A Range |
| /6 | 252.0.0.0 | 3.255.255.255 | 67,108,864 | 67,108,862 | Class A Range |
| /7 | 254.0.0.0 | 1.255.255.255 | 33,554,432 | 33,554,430 | Class A Range |
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,216 | 16,777,214 | Class A Range |
| /9 | 255.128.0.0 | 0.127.255.255 | 8,388,608 | 8,388,606 | Class B Range |
| /10 | 255.192.0.0 | 0.63.255.255 | 4,194,304 | 4,194,302 | Class B Range |
| /11 | 255.224.0.0 | 0.31.255.255 | 2,097,152 | 2,097,150 | Class B Range |
| /12 | 255.240.0.0 | 0.15.255.255 | 1,048,576 | 1,048,574 | Class B Range |
| /13 | 255.248.0.0 | 0.7.255.255 | 524,288 | 524,286 | Class B Range |
| /14 | 255.252.0.0 | 0.3.255.255 | 262,144 | 262,142 | Class B Range |
| /15 | 255.254.0.0 | 0.1.255.255 | 131,072 | 131,070 | Class B Range |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,536 | 65,534 | Class B Range |
| /17 | 255.255.128.0 | 0.0.127.255 | 32,768 | 32,766 | Class C Range |
| /18 | 255.255.192.0 | 0.0.63.255 | 16,384 | 16,382 | Class C Range |
| /19 | 255.255.224.0 | 0.0.31.255 | 8,192 | 8,190 | Class C Range |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,096 | 4,094 | Class C Range |
| /21 | 255.255.248.0 | 0.0.7.255 | 2,048 | 2,046 | Class C Range |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,024 | 1,022 | Class C Range |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 | Class C Range |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 | Class C Range |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 | Standard |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 | Standard |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 | Standard |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 | Standard |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 | Standard |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 | Standard |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 | Point-to-Point (RFC 3021) |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 | Host Route |
Calculating Usable Hosts & Network Bits
To calculate usable host capacity for any prefix length P (from /1 to /30):
Total Addresses = 2^(32 - P) Usable Hosts = 2^(32 - P) - 2
Example for 192.168.1.0/24: 2^(32 - 24) = 2^8 = 256 total addresses. Subtracting Network (192.168.1.0) and Broadcast (192.168.1.255) yields 254 usable hosts.
IP Subnetting for AWS, Azure, and GCP VPCs
Cloud Reserved IP Addresses Notice
Major cloud providers reserve specific IP addresses in every VPC subnet. For example, AWS reserves 5 IP addresses per subnet (Network, VPC Router, DNS Server, Future Use, and Broadcast). A /24 VPC subnet in AWS provides 251 usable EC2 IPs instead of the standard 254.
Common Subnetting Mistakes & Errors
Subnetting Pitfalls
- Non-Contiguous Subnet Masks: Subnet masks must contain contiguous 1 bits followed by 0 bits. Masks like
255.255.240.128are invalid. - Host Bits Set in Network Inputs: Entering an IP like
192.168.1.50/24automatically calculates the base Network Address as192.168.1.0. - Overlapping VPC Subnets: Ensure IP ranges do not overlap across cloud regions or VPN tunnel endpoints.
Frequently Asked Questions
References & Standards
RFC 4632: Classless Inter-domain Routing (CIDR) Specification
IETF standard specification for CIDR subnet allocation and IPv4 routing architecture.
RFC 4291: IP Version 6 Addressing Architecture
Official standard specification for IPv6 address prefixes and subnet masks.
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