IPv4 IP to Subnet Mask Calculator
Use this free tool to convert a CIDR prefix (like /24) into a subnet mask and instantly calculate the network range for any IPv4 address.
What this IP to subnet mask calculator does
When you enter an IP address and a prefix length, this calculator gives you the exact subnet mask plus key subnet details you normally have to compute by hand. It is useful for network engineers, students, IT admins, and anyone configuring routers, firewalls, cloud VPCs, VPNs, or local LANs.
Instead of manually converting binary bits, you get immediate results for:
- Subnet mask (for example,
255.255.255.0) - Wildcard mask (useful for ACLs)
- Network ID and broadcast address
- Usable host range and host counts
- Binary subnet mask format for quick verification
Quick refresher: IP, subnet mask, and CIDR
IPv4 address
An IPv4 address contains 32 bits split into four octets, such as 192.168.1.10.
Subnet mask
A subnet mask tells you which part of an IP address is the network portion and which part is the host portion. Example: 255.255.255.0.
CIDR notation
CIDR is a shorter way of writing masks. /24 means the first 24 bits are network bits. The equivalent subnet mask is 255.255.255.0.
How to use this calculator
- Enter an IPv4 address in dotted format.
- Enter the CIDR prefix from 0 to 32 (with or without a slash).
- Click Calculate.
- Review subnet mask, network range, and host details.
If your input is invalid, you’ll get a clear error message so you can correct it quickly.
Common CIDR to subnet mask conversions
| CIDR | Subnet Mask | Total Addresses | Typical Use |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | Very large internal allocations |
| /16 | 255.255.0.0 | 65,536 | Large enterprise segments |
| /24 | 255.255.255.0 | 256 | Small LAN/VLANs |
| /30 | 255.255.255.252 | 4 | Legacy point-to-point links |
| /31 | 255.255.255.254 | 2 | Modern point-to-point routing |
| /32 | 255.255.255.255 | 1 | Single host route |
Why this matters in real networks
Subnetting is not just a certification topic. Correct subnet calculations improve routing efficiency, reduce broadcast traffic, and prevent IP conflicts. Whether you are creating security zones, assigning DHCP scopes, or troubleshooting connectivity issues, converting IP and CIDR to a proper subnet mask is a core networking skill.
Frequent mistakes to avoid
- Using a mask that does not match your planned host count
- Accidentally assigning the network ID or broadcast address to a device
- Mixing up wildcard masks and subnet masks in ACL rules
- Forgetting that /31 and /32 have special behavior
FAQ
Can I use this as a CIDR calculator?
Yes. It acts as a CIDR to subnet mask calculator and also gives network/broadcast details.
Does it support private and public IPs?
Yes. The math works for any valid IPv4 address. The output also indicates whether the entered IP is in common private ranges.
Is this useful for cloud networking?
Absolutely. It helps with VPC subnet planning in AWS, Azure, GCP, and on-prem network design.
Final thoughts
If you work with IPv4 addressing, this IP to subnet mask calculator can save time and prevent costly misconfigurations. Keep it bookmarked as your quick subnetting reference for network planning, lab work, and day-to-day operations.