Subnet Calculator – IPv4 CIDR, VLSM Split & IPv6, Free

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Subnet Calculator

Enter any IPv4 address with CIDR notation for the complete breakdown — network address, broadcast, usable host range, wildcard mask, host counts — plus binary masks, IP class and type detection. Split networks with the VLSM divider and calculate IPv6 subnets too. Instant, offline, private.

✓ Full CIDR Breakdown · ✓ Binary Mask · ✓ VLSM Splitter · ✓ IPv6 · ✓ /31 //32 Correct

🔧 JS ⏳ · Input — · Result — · Engine ⏳

IPv4 address with CIDR

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Network address

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Broadcast address

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Subnet mask

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Wildcard mask

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First usable host

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Last usable host

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Total addresses

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Usable hosts

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IP class / type

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🔢 Binary & Hex

Subnet mask (binary)

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IP (binary)

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IP (hex)

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Network to split (CIDR)

New prefix length

Example: /24 split into /26s = 4 equal subnets of 62 hosts each.

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#	Network	First host	Last host	Broadcast	Usable

IPv6 address with prefix

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Expanded address

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Prefix

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Network (first hextets)

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Total addresses in subnet

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Type

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Interface ID bits

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CIDR Subnet Reference Table

CIDR	Subnet mask	Total addresses	Usable hosts	Typical use
/8	255.0.0.0	16,777,216	16,777,214	Legacy class A
/16	255.255.0.0	65,536	65,534	Large networks
/20	255.255.240.0	4,096	4,094	Large office
/22	255.255.252.0	1,024	1,022	Medium office
/24	255.255.255.0	256	254	Standard LAN ⭐
/25	255.255.255.128	128	126	Half LAN
/26	255.255.255.192	64	62	Small dept
/27	255.255.255.224	32	30	Small group
/28	255.255.255.240	16	14	Small cluster
/29	255.255.255.248	8	6	Point links + spare
/30	255.255.255.252	4	2	Point-to-point
/31	255.255.255.254	2	2 (RFC 3021)	P2P modern
/32	255.255.255.255	1	1 (host route)	Single device

How Subnetting Math Works

A subnet mask splits an IPv4 address into a network portion (identifying the subnet) and a host portion (identifying the device within it). The number of 1-bits in the mask is the CIDR prefix — a /26 mask has 26 one-bits followed by 6 zero-bits (255.255.255.192).

The four key operations: Network address = IP AND mask (all host bits zeroed). Broadcast address = IP OR wildcard (all host bits set to 1). Usable hosts = total addresses minus the network and broadcast addresses — except /31 point-to-point links, which use both addresses per RFC 3021, and /32 single-host routes. Example: 192.168.1.130/26 → network 192.168.1.128, broadcast 192.168.1.191, usable range .129–.190, 62 hosts. The binary panel above shows the AND operation bit by bit — the exact skill CCNA exams test.

Why Use This IP Subnet Calculator?

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Complete CIDR Breakdown

Network, broadcast, range, wildcard, counts, class and type in a single pass.

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Binary + Hex Views

Mask and IP in binary — the CCNA-study detail most calculators skip.

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VLSM Splitter

Divide any network into equal subnets by new prefix — full list generated.

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IPv6 Support

Expansion, network portion, address counts and type detection for v6.

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100% Private

IPs stay in your browser — internal addresses never sent anywhere.

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Instant & Offline

Pure bit math on every keystroke — works at client sites with no signal.

Popular Use Cases

• 🌐 Design subnets for office networks and VLANs
• 🎓 Practice for CCNA, Network+ and cloud certification exams
• ☁️ Plan cloud VPC subnet ranges (AWS, Azure, GCP)
• 🔧 Troubleshoot "why can't these two hosts talk" mask mismatches
• 🏢 Split acquired IP space into usable department blocks
• 🔐 Verify ACL and firewall wildcard masks match intent

Pro Tips for Subnetting

• Memorize the block sizes: /24 = 256, /25 = 128, /26 = 64, /27 = 32, /28 = 16, /29 = 8, /30 = 4. Network addresses always start on those boundaries — 192.168.1.130/26 lands in the .128 block.
• /31 is legit: RFC 3021 made two-address point-to-point links standard — older cheat sheets saying "/31 has 0 usable hosts" are outdated. This calculator handles it correctly.
• Wildcard = inverted mask: ACLs and routing configs use wildcards (0.255.255.255 for /8). The calculator provides it so you don't hand-invert octets under pressure.
• Private ranges quick check: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — plus loopback 127/8, link-local 169.254/16, and CGNAT 100.64/10. The tool detects all of these.
• IPv6 prefixes work in nibbles: prefixes move in 4-bit steps for clean boundaries — a /64 is the standard LAN size, effectively inexhaustible per site.

Frequently Asked Questions

A tool that takes an IP address with its CIDR prefix and computes everything the network engineer needs: the network and broadcast addresses, usable host range, subnet and wildcard masks, host counts, and related details — instantly and without bit-math mistakes.

The CIDR number is how many 1-bits the mask has. Fill them from the left in each of four octets: /26 = 26 ones = 255.255.255.192. Enter any IP with its CIDR above and the mask appears automatically — along with its binary form.

64 total addresses, minus the network and broadcast addresses = 62 usable hosts. The general rule is 2 to the power of host bits, minus 2 — except /31 point-to-point links (2 usable, per RFC 3021) and /32 single-host routes.

The subnet mask with every bit inverted — used in ACLs and some routing configs to match address ranges. A /24 mask of 255.255.255.0 becomes the wildcard 0.0.0.255. This calculator provides it alongside the mask.

Variable Length Subnet Masking — dividing a network into subnets of different sizes instead of equal ones, so a 60-host department doesn't waste a 500-host block. The VLSM tab splits a network into equal parts by prefix; chain it for size-mixed designs.

Yes — the IPv6 tab expands compressed addresses, shows the network portion for your prefix, computes the subnet size and detects the address type (global, link-local, unique-local, multicast, loopback).

The first octet decides: 1–126 Class A, 128–191 Class B, 192–223 Class C (127 is loopback). Classes are legacy for exams — modern networks use CIDR — but the tool reports the class plus whether the address is private, loopback, link-local or public.

No. All bit math runs in your browser with JavaScript — internal addresses like 10.x or 192.168.x stay on your device, nothing is transmitted, stored, or logged. Refreshing clears everything.