IPv4 Mask Calculator
Enter an IPv4 address and either a CIDR prefix or subnet mask to calculate network details instantly.
What Is a Mask Calculator?
A mask calculator is a networking tool that helps you understand how an IP address is divided into
network and host portions. In IPv4, this division is described by a
subnet mask (like 255.255.255.0) or CIDR notation (like /24).
If you work with routers, firewalls, cloud networks, or even home labs, mask calculations are essential. A good calculator saves time and prevents common mistakes when planning address ranges, assigning hosts, and defining VLANs or subnets.
Why Subnet Masks Matter
Every device in an IPv4 network has an address. But that address only makes sense when paired with a mask. The mask tells the device:
- Which part of the address identifies the network
- Which part identifies the individual host
- What broadcast address belongs to that subnet
- Which addresses are valid for hosts
Without the correct mask, traffic can be misrouted, hosts may become unreachable, and troubleshooting becomes much harder than it needs to be.
How to Use This Calculator
Step 1: Enter an IPv4 address
Provide a valid IPv4 address, such as 10.0.5.120 or 172.16.2.9.
Step 2: Enter either CIDR or a dotted mask
You can use CIDR (/23, /27, etc.) or a standard dotted mask
(255.255.254.0, 255.255.255.224, etc.). If you provide both, the dotted mask
is used and the prefix is derived automatically.
Step 3: Review the computed subnet details
You will get the network address, broadcast address, wildcard mask, first and last usable host, total addresses, usable host count, and address classification.
Common CIDR and Mask Reference
| CIDR | Subnet Mask | Total Addresses | Usable Hosts* |
|---|---|---|---|
| /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 |
*For traditional subnets. /31 and /32 are special cases.
Worked Example
Input
IP: 192.168.1.34, Prefix: /24
Output Summary
- Network:
192.168.1.0 - Broadcast:
192.168.1.255 - Usable Host Range:
192.168.1.1 - 192.168.1.254 - Usable Hosts:
254
This means every address from .1 to .254 can be assigned to hosts in that subnet.
The .0 address identifies the network, and .255 is reserved for broadcast.
Frequent Mistakes to Avoid
- Using non-contiguous masks: A valid subnet mask must have all 1s on the left and all 0s on the right.
- Mixing CIDR and dotted mask incorrectly: Make sure they represent the same network size.
- Assigning network/broadcast addresses to hosts: These are reserved in most subnet designs.
- Forgetting special cases: /31 and /32 do not behave like traditional LAN subnets.
Final Thoughts
A subnet mask calculator is one of those simple tools that pays off every day in network administration. Whether you are configuring a home lab, planning enterprise VLANs, or checking cloud VPC ranges, accurate mask math helps you avoid outages and design cleaner networks.
Use the calculator above whenever you need fast, reliable subnet details from an IPv4 address and mask.