IP Subnet Calculator: IPv4, IPv6 and CIDR
Calculate network details, IP ranges, and usable hosts from an IPv4 or IPv6 address and CIDR mask.
Input
Quick Tip
The most common subnet masks are /24 for home networks (255.255.255.0) and /32 for single hosts.
Ready to Calculate
Enter an IP address and select a CIDR prefix to see detailed network information.
How do I find a subnet mask and usable host range?
Choose IPv4 or IPv6, enter the address, and select an integer CIDR prefix. For IPv4, inspect the network, broadcast address, mask, and host range. Use standard colon-separated IPv6 notation; embedded dotted-IPv4 IPv6 addresses are a known limitation of the current parser.
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How to use this calculator
Understanding IP Subnetting
Subnetting is the practice of dividing a network into two or more smaller networks. It increases routing efficiency, enhances network security, and reduces broadcast domain size.
IPv4: An address consists of 32 bits, divided into a **Network ID** and a **Host ID**. The **Subnet Mask** (e.g., 255.255.255.0) determines where the split occurs.
IPv6: An address consists of 128 bits. Subnetting is simpler because there is no variable-length subnet mask in the same way as IPv4. Instead, a **Prefix Length** (e.g., `/64`) is used to denote the network portion. Standard subnetting in IPv6 almost always uses a `/64` prefix for end-user networks.
Common IPv4 CIDR Reference
| CIDR | Subnet Mask | Total Hosts |
|---|---|---|
| /32 | 255.255.255.255 | 1 (Single Host) |
| /30 | 255.255.255.252 | 4 (2 Usable) |
| /24 | 255.255.255.0 | 256 (254 Usable) |
| /16 | 255.255.0.0 | 65,536 (65,534 Usable) |
| /8 | 255.0.0.0 | 16.7 Million |
Common IPv6 Prefixes
| Prefix | Typical Usage | Address Count |
|---|---|---|
| /128 | Single Host (Loopback, etc.) | 1 |
| /64 | Standard LAN Subnet | 18 Quintillion (2^64) |
| /56 | Typical Home/Small Business Assignment | 256 x /64 Subnets |
| /48 | Large Organization Assignment | 65,536 x /64 Subnets |
| /32 | ISP Allocation | 4 Billion x /64 Subnets |