/27 Subnet Calculator

A /27 subnet is a block of 32 IPv4 addresses with 30 usable hosts. This page calculates which /27 block an IP address belongs to and lists every /27 subnet inside a bigger network you enter. The calculator runs in your browser, is free, and needs no sign-up. Enter an address and a parent network, and the results update as you type. Every answer on this page is about /27 blocks, because the prefix length is fixed at 27. To split a network into a different size, use the main subnet calculator instead.

A /27 has the mask 255.255.255.224 and the wildcard 0.0.0.31.

A /27 is a popular VLAN size because 30 hosts suit one office team or one access switch.

How to use the /27 subnet calculator

1. In the IP address field, type an IPv4 address, such as 192.168.10.77. Leading zeros and values above 255 are rejected.
2. In the Parent network (CIDR) field, type the bigger network you want to split, such as 192.168.10.0/24. Its prefix must be 27 or shorter.
3. Read the primary results. The first line gives the /27 block that contains your IP, and the next line gives its usable host range.
4. Open How it was calculated under the result to see the formula, the values it used and the answer.
5. Scroll the subnet table to find every /27 in the parent, with its network address, first and last host, and broadcast address.

You can click a preset chip above the form, such as “Home / office LAN”, to load a typical case. Click Reset to return to the starting example. If you need a different starting point in the table, open More options and enter a subnet number in Start the table at subnet number. The table shows 256 rows at a time, so a parent with more than 256 subnets needs the next page.

Example: in 192.168.10.0/24 the eight /27 blocks start at .0, .32, .64, .96, .128, .160, .192 and .224; 192.168.10.77 is in 192.168.10.64/27.

Copy link keeps the IP and parent in the address, and Print / save as PDF gives a one-page record with the table.

What is the /27 subnet mask?

A /27 prefix keeps the first 27 bits of the address for the network and leaves 5 bits for hosts. Written out, the mask is 11111111.11111111.11111111.11100000, which is 255.255.255.224 in dotted decimal; the wildcard (inverse) mask used in router access lists is 0.0.0.31. Each /27 block holds 2^5 = 32 addresses. The first is the network address and the last is the broadcast address (RFC 950), so 30 are usable hosts.

How do you find the /27 subnet of an IP address?

The mask stops being 255 in the fourth octet, and the block size there is 256 − 224 = 32. Round that octet of the address down to a multiple of 32, keep the octets before it and set the octets after it to 0. For 192.168.10.77, the fourth octet is 77; 77 ÷ 32 rounds down to 2, and 2 × 32 = 64. The network is therefore 192.168.10.64/27, the usable hosts run from 192.168.10.65 to 192.168.10.94, and the broadcast address is 192.168.10.95.

How many /27 subnets fit in a larger network?

Each step of one bit doubles the count, so a /24 holds 2^(27 − 24) = 8 subnets of size /27. In 192.168.10.0/24 they start at 192.168.10.0 and go up in steps of 32 in the fourth octet, to 192.168.10.224/27; 192.168.10.64/27 is number 3. The table on this page lists them with their first host, last host and broadcast address, 256 rows at a time.

How does a /27 compare with the sizes next to it?

One bit shorter, a /26 doubles the block to 64 addresses (62 usable hosts); one bit longer, a /28 halves it to 16 addresses (14 usable hosts). Two neighbouring /27 blocks can be joined into one /26 only when the first of them starts on a multiple of 64 in the fourth octet — 192.168.10.64/26 contains 192.168.10.64/27, 192.168.10.96/27.

How is a /27 written in different configurations?

The same mask appears in several forms depending on the device or file: CIDR notation /27 (most routers, cloud consoles and firewalls), dotted decimal 255.255.255.224 (older interface settings, DHCP), hexadecimal 0xFFFFFFE0 (some Unix tools such as ifconfig on BSD), and the wildcard 0.0.0.31 in router access lists and OSPF network statements. They all describe the same 32-address block.

Where is a /27 used?

A /27 suits a small office floor, a Wi-Fi guest network or a VLAN of up to 30 devices.

Worked examples

Calculated by the tool above with these values.

Frequently asked questions

What is the subnet mask for a /27?

255.255.255.224, with wildcard mask 0.0.0.31. In binary the mask is 11111111.11111111.11111111.11100000.

How many usable hosts does a /27 have?

30. A /27 has 32 addresses in total, and the network and broadcast addresses are not assigned to hosts.

How many /27 subnets are in a /24?

Eight. A /24 has 256 addresses and each /27 takes 32, so the network addresses in the last octet are 0, 32, 64, 96, 128, 160, 192 and 224.

What is the first and last usable IP address in a /27?

The first usable address is the network address + 1 and the last is the broadcast address − 1. For 192.168.10.64/27 that is 192.168.10.65 to 192.168.10.94.

What does the warning about host bits mean?

The parent network you typed is not a network address (it has host bits set), so the calculator rounds it down to its network address and says so.

Is the calculator free, and is anything I type uploaded?

Yes, it is free, needs no sign-up, and every calculation runs in your browser; nothing you type is uploaded. Results may be used in any work, including commercial projects, without attribution.

Can I print or share a calculation?

Yes. Print / save as PDF gives a one-page record with the inputs, results, steps and date, and Copy link stores your inputs in the page address so the same calculation reopens later.

Related tools

• Subnet cheat sheet: Use it when you want a quick reference for common prefix lengths and block sizes.
• Subnetting practice: Use it to test yourself on working out subnet boundaries by hand.
• Subnet mask calculator: Use it when you need the mask, wildcard or binary form for a different prefix.
• /29 subnet mask: Use it when you need blocks of 8 addresses instead of 32.
• /22 subnet: Use it when you want to see how a larger block splits into /27 subnets.
• Private IP address ranges: Use it to check which address ranges are reserved for private networks before you choose a parent.