Free IP Subnet
Calculator.
Calculate network addresses, broadcast, host ranges, wildcard masks, and more — for both IPv4 and IPv6. Instantly.
Enter IP Address
Enter an IPv4 address with a CIDR prefix or subnet mask.
Enter IPv6 Address
Enter an IPv6 address with prefix length (e.g. 2001:db8::/32).
Every feature you need.
Nothing you don't.
Built for network engineers, developers, and students who need fast, accurate subnet calculations without the noise.
IPv4 & IPv6
Full support for both IPv4 subnet calculations and IPv6 prefix operations. Switch instantly between modes.
Binary Visualizer
See every address in binary — network bits highlighted in blue, host bits in gray. Understand subnetting visually.
Shareable URLs
Every calculation updates the URL. Share a link with your team or bookmark a specific subnet for later.
15+ Output Fields
Network, broadcast, host range, subnet mask, wildcard, hex, integer, PTR record, IPv4-mapped IPv6, and more.
Subnet Splitter
Instantly see all subnets if you split the current network by one bit. Perfect for network planning.
100% Free
No account, no paywall, no rate limits. All calculations run in your browser — your data never leaves your device.
IPv4 CIDR Chart.
The most common prefix lengths and their host counts at a glance. See the full CIDR chart for all /1–/32 values.
| CIDR | Subnet Mask | Wildcard Mask | Total Addresses | Usable Hosts | Notes |
|---|---|---|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,216 | 16,777,214 | Class A |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,536 | 65,534 | Class B |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 | Class C — most common |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 | Half /24 |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 | Quarter /24 |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 | |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 | Common in cloud VPCs |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 | |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 | Point-to-point links |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 | RFC 3021 — P2P only |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 | Host route |
What is a subnet mask?
A subnet mask is a 32-bit number that divides an IP address into anetwork portion (which identifies the network) and a host portion(which identifies the individual device).
Written in dotted-decimal notation, common masks look like255.255.255.0 (for a /24 network) or255.255.0.0 (for a /16 network).
CIDR notation (Classless Inter-Domain Routing) expresses the same information more compactly — 192.168.1.0/24 means the first 24 bits are the network part.
The wildcard mask is the bitwise inverse of the subnet mask. Used in Cisco ACLs and OSPF configurations to specify which bits to "care about."
Quick Glossary
- Network Address
- First address in a subnet. Identifies the network itself — never assigned to a host.
- Broadcast Address
- Last address in a subnet. Packets sent here reach all hosts on the network.
- Wildcard Mask
- Bitwise NOT of subnet mask. Used in Cisco ACLs and OSPF to match address ranges.
- VLSM
- Variable Length Subnet Masking — using different-sized subnets within the same network to save address space.
- PTR Record
- Reverse DNS lookup record. Maps an IP address back to a hostname, stored in in-addr.arpa.
The Free Netmask Calculator Built for Network Engineers.
Our netmask calculator is a free, browser-based tool designed to help network engineers, developers, students, and IT administrators instantly compute all key properties of any IPv4 or IPv6 subnet. Whether you need to determine a network address, find the broadcast address, calculate usable host ranges, or convert between CIDR notation and subnet mask formats, this subnet mask calculator does it all in a single click — with no login, no ads, and no rate limits.
What Is a Netmask and Why Does It Matter?
A netmask (also called a subnet mask or network mask) is a 32-bit binary mask used to divide an IP address into its network and host portions. In IPv4, it is typically written in dotted-decimal notation — for example, 255.255.255.0 — or in CIDR notation as /24. The netmask tells routers and devices which part of an IP address identifies the network segment and which part identifies the individual host. Without a proper netmask, IP routing, subnetting, and network segmentation would be impossible.
Understanding netmasks is fundamental to network design. When you configure a server, a cloud VPC, a firewall rule, or a router interface, you almost always need to specify a subnet mask or CIDR prefix. OurIP netmask calculator removes the guesswork, giving you every value you need in milliseconds.
How to Use the Subnet Mask Calculator
Using this netmask calculator online is straightforward. Enter any IPv4 address in the IP Address field — for example, 192.168.1.0. Then select a CIDR prefix from the dropdown (e.g. /24) or type the subnet mask directly (e.g. 255.255.255.0). Both inputs are synchronised automatically. Click Calculate (or press Enter) and the tool instantly computes:
- Network Address — the base address of the subnet
- Broadcast Address — the last address in the subnet
- Usable Host Range — the first and last assignable host IPs
- Subnet Mask & Wildcard Mask — in dotted-decimal format
- Total & Usable Host Count — exactly how many devices fit in the subnet
- Binary Representation — shows network vs host bits visually
- Hex, Integer, PTR Record, IPv4-Mapped IPv6, 6to4 Prefix — for advanced use
You can also paste a CIDR address directly into the IP field (e.g. 10.0.0.0/8) and the tool parses both fields automatically. Every result has a copy-to-clipboard button for instant use in configuration files, documentation, or firewall rules.
CIDR Notation Explained
CIDR notation (Classless Inter-Domain Routing) is a compact way to express an IP address and its network prefix length in a single string — for example, 192.168.0.0/16. The number after the slash represents how many bits of the 32-bit address are the network portion. CIDR replaced the old Class A/B/C system in 1993, allowing much more efficient allocation of IP address space. Oursubnet mask to CIDR calculator converts between both representations automatically.
IPv6 Calculator Support
The tool also functions as a full IPv6 calculator. Switch to the IPv6 tab, enter any IPv6 address and prefix length, and get the expanded/compressed form, network prefix, address type (Global Unicast, Link-Local, Unique Local, Multicast, etc.), total address count, and the ip6.arpa reverse DNS zone. Both compressed (2001:db8::/32) and full (2001:0db8:0000:0000:0000:0000:0000:0000) formats are accepted.
Subnet Splitter & CIDR Chart
Beyond single-subnet calculations, this subnet netmask calculator includes a built-in subnet splitter that shows all sub-subnets if you divide the current block by one prefix bit. This is ideal for VLSM (Variable Length Subnet Masking) network planning. We also offer a dedicatedCIDR chart page listing every prefix from /1 to /32 with subnet mask, wildcard mask, total addresses, and usable host count — a handy reference for any network engineer.
Shareable URLs & Privacy
Every calculation is reflected in the page URL (e.g. ?ip=192.168.1.0&cidr=24), making it easy to share a specific subnet with teammates or bookmark frequently used networks. All calculations run entirely in your browser using JavaScript — no data is ever sent to a server, and we do not store or log any IP addresses you enter.
Frequently Asked Questions.
Common questions about netmask calculators, subnet masks, CIDR notation, and IP networking.
255.255.255.0 (CIDR /24) means the first 24 bits identify the network and the last 8 bits identify the host. Netmasks are fundamental to IP routing, firewall rules, VPN configurations, and cloud network design.255.255.255.0 is the most common subnet mask, equivalent to CIDR /24. It allocates 24 bits for the network and 8 bits for hosts, giving 256 total addresses per subnet — with 254 usable host addresses. The network address (e.g. 192.168.1.0) and the broadcast address (e.g. 192.168.1.255) are reserved. This mask is used in the majority of home, office, and small business networks.11111111.11111111.11111111.00000000 → 255.255.255.0. (4) AND the IP with the mask to get the network address. (5) OR the network with the inverted mask (wildcard) to get the broadcast. Our IP netmask converter does all of this instantly — just enter an IP and prefix.10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) for internal use only; Loopback — 127.0.0.1 (IPv4) or ::1 (IPv6) for self-communication; and Link-Local — 169.254.0.0/16 automatically assigned when DHCP is unavailable.0.0.0.0 0.0.0.0 (also written as 0.0.0.0/0) is the default route — also called the gateway of last resort. It matches any destination IP address that has no more specific match in the routing table. Packets without a matching route are forwarded via this default — typically toward the internet gateway or upstream ISP router. In Cisco IOS, it's configured as ip route 0.0.0.0 0.0.0.0 [next-hop].255.255.255.252 equals CIDR /30. It provides just 4 IP addresses per subnet: the network address, 2 usable hosts, and the broadcast address. This is the standard mask for point-to-point links between two routers — exactly 2 usable IPs are all that's needed. Example: network 192.168.1.0/30 gives hosts 192.168.1.1 and 192.168.1.2, with broadcast at 192.168.1.3.255.255.240.0. A /20 block spans 16 consecutive Class C (/24) networks. It is commonly used in medium-to-large enterprise networks and cloud VPC configurations (e.g. AWS, GCP, Azure) where thousands of IPs are needed in one segment.255.255.255.248 corresponds to CIDR /29, providing 8 total addresses per subnet and 6 usable host addresses (8 − 2 for network and broadcast). This is a common choice for small server segments, network printer subnets, or management VLANs where only a handful of devices need IP addresses. Block size is 8, so subnets increment by 8: .0, .8, .16, .24 …192.168.1.0 is the network address of the 192.168.1.0/24 subnet (subnet mask 255.255.255.0). It identifies the subnet itself and cannot be assigned to a host. The usable host range is 192.168.1.1 – 192.168.1.254, and the broadcast address is 192.168.1.255. The 192.168.0.0/16 block is a private RFC 1918 range — not routable on the public internet, making it the standard choice for home and office LANs.Start calculating in seconds.
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