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IPv4 Subnet Calculator

Get every subnet detail you need at a glance — network and broadcast addresses, usable host range, subnet mask, wildcard mask, binary representation, and network classification. Updates live as you type or drag the prefix slider. Built by Datastrive, a Chicago managed IT and cybersecurity provider.

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/24

Quick reference: common subnet sizes

The most useful prefixes for office networks, lab segments, and point-to-point links. Click any row in the calculator above to verify the math, or copy the mask straight into your switch or firewall config.

CIDR Subnet mask Wildcard Total addresses Usable hosts Typical use
/16255.255.0.00.0.255.25565,53665,534Large enterprise / aggregation
/20255.255.240.00.0.15.2554,0964,094Mid-sized campus / data center
/22255.255.252.00.0.3.2551,0241,022Large office / multi-floor VLAN
/23255.255.254.00.0.1.255512510Office VLAN with growth headroom
/24255.255.255.00.0.0.255256254Standard office or VLAN
/25255.255.255.1280.0.0.127128126Half a /24 (split for VLAN)
/26255.255.255.1920.0.0.636462Small department or IoT VLAN
/27255.255.255.2240.0.0.313230Small VLAN, server segment
/28255.255.255.2400.0.0.151614Management / DMZ segment
/29255.255.255.2480.0.0.786Small DMZ / hosted IPs
/30255.255.255.2520.0.0.342Point-to-point link
/31255.255.255.2540.0.0.122*Point-to-point (RFC 3021)
/32255.255.255.2550.0.0.011Single host route

How to plan IP addressing for a business network

The math is the easy part. The harder part is planning an IP scheme that doesn’t paint you into a corner two years from now when you add a new VLAN, a guest network, or a second site. Here’s the order of operations that holds up.

  1. Start with private (RFC 1918) ranges Use 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 for everything internal. 10.0.0.0/8 gives you the most room and is the cleanest choice for a multi-site or growing organization. Reserve 192.168.0.0/16 for very small environments or home use to avoid conflicts when staff connect VPNs from home networks.
  2. Allocate /24 by default for office VLANs A /24 (254 usable hosts) is the right unit of allocation for most office VLANs because it’s mentally simple, easy to whiteboard, and leaves headroom. Going smaller saves nothing meaningful. Going larger usually means you should be splitting into multiple VLANs anyway.
  3. Plan VLANs by function, not by floor Separate VLANs for users, voice, IoT, printers, guest, servers, and management. Each gets its own /24. This is the foundation that lets you apply different firewall rules, QoS, and broadcast domains. A flat /20 with everything mixed together is the worst of all worlds — less secure, harder to troubleshoot, and harder to grow.
  4. Reserve management addresses outside DHCP For each VLAN, carve out a static range at the bottom for infrastructure: gateway at .1, switches and APs from .2–.20, servers and printers .21–.50, then DHCP from .100–.250. The exact split depends on the network, but have a convention and stick to it across all your VLANs.
  5. Use /30 (or /31) for point-to-point links Router-to-router, firewall-to-firewall, MPLS handoffs, or any link with exactly two endpoints should use a /30 (2 usable hosts) or /31 (RFC 3021, both addresses usable). Allocating a /24 to a point-to-point link wastes 252 addresses and obscures your topology in IP audits.
  6. Document the plan in one place A spreadsheet or IPAM tool listing every subnet, its purpose, VLAN ID, gateway, and DHCP scope is worth more than any monitoring dashboard the day you’re troubleshooting at 2 AM. Without documentation, your network is whatever the last person to touch it remembered. With it, anyone can understand the design.

Frequently asked questions

What’s the difference between /24 and 255.255.255.0?

They mean the exact same thing in different notations. /24 is CIDR notation: the leading 24 bits of the address are the network portion, and the remaining 8 bits identify hosts within that network. 255.255.255.0 is dotted-decimal subnet mask notation: in binary it’s twenty-four 1s followed by eight 0s — the 1s mark the network bits, the 0s mark the host bits.

CIDR is preferred in modern documentation because it’s shorter and unambiguous. Older networking gear and Windows still expose dotted-decimal masks in their UIs.

How many usable hosts are in a /27?

A /27 has 32 total addresses (2 to the 5th power, since 32 – 27 = 5 host bits) and 30 usable hosts. The first address is reserved as the network address and the last is the broadcast address — neither can be assigned to a host.

The general formula: usable = 2^(32-prefix) − 2 for any prefix from /1 through /30. A /31 is a special case (RFC 3021) used for point-to-point links where both addresses are usable. A /32 is a single-host route.

What are the private IP address ranges?

RFC 1918 reserves three ranges for private networks — addresses that won’t be routed across the public internet:

10.0.0.0/8 (10.0.0.0 through 10.255.255.255) — about 16.7 million addresses, ideal for medium to large organizations.

172.16.0.0/12 (172.16.0.0 through 172.31.255.255) — about 1 million addresses, often used by Docker and other infrastructure tools.

192.168.0.0/16 (192.168.0.0 through 192.168.255.255) — about 65,000 addresses, the default for home routers and small offices.

What’s a wildcard mask and when do I use one?

A wildcard mask is the bitwise inverse of a subnet mask. Where a subnet mask has 1s, a wildcard mask has 0s, and vice versa. For 255.255.255.0 the wildcard is 0.0.0.255.

Wildcard masks are used in Cisco access control lists (ACLs) and OSPF area definitions. The 0 bits mean “must match exactly” and the 1 bits mean “don’t care.” So 10.0.0.0 0.0.0.255 in an ACL matches any address in 10.0.0.0/24.

What’s VLSM and why does it matter?

VLSM stands for Variable Length Subnet Masking — using different subnet sizes within the same parent network. Instead of allocating every VLAN a /24, you might give your user VLAN a /23, your printer VLAN a /27, and your point-to-point links /30s.

VLSM lets you allocate address space efficiently without waste. It’s especially useful inside a /16 where you’re carving out dozens of subnets of different sizes. Modern routing protocols (OSPF, EIGRP, BGP) all support VLSM natively.

Should small businesses bother with IPv6?

For internal networks, not yet for most. The combination of NAT plus RFC 1918 IPv4 still works fine for typical office use, and IPv6 adds complexity that pays off mostly when you’re running services exposed to the public internet or when you’ve actually hit IPv4 scaling limits.

That said, your ISP’s internet connection is increasingly likely to deliver IPv6 by default, and dual-stack on the WAN side is a reasonable place to start. Internal IPv6 is worth doing when you’re either at a scale where you need it, or when you’re refreshing infrastructure and have time to do it right.

Need help designing your network?

From single-office VLAN planning to multi-site WAN architectures and structured cabling for new buildouts, Datastrive handles the design, implementation, and ongoing management. We’re a Chicago-based managed IT provider serving small and mid-sized businesses across the region.

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