Lan Calculator
Designing a local area network starts with a simple question: how big should the subnet be? Too small and you run out of addresses; too large and you waste address space and create an oversized broadcast domain. The LAN Calculator answers that question in seconds: enter your network address and the number of hosts you need, and it recommends the ideal subnet size with the full address breakdown.
Why Right-Sizing Your LAN Matters
Every device on a LAN shares the same broadcast domain, which means broadcast traffic reaches every host. Keeping the subnet right-sized limits that overhead while leaving enough spare addresses for growth. A LAN that is too small forces a painful renumbering later; one that is too large wastes addresses and can degrade performance. Getting the size right from the start saves time, avoids outages, and makes the network easier to document and secure.
How to Use the LAN Calculator
Sizing your LAN takes three inputs and one click:
- Enter the network IP address. Type the base address of your planned network, for example 192.168.0.0.
- Enter the number of hosts needed. Count every device that needs an address: computers, phones, printers, cameras, access points, and a margin for growth.
- Click Calculate. The tool finds the smallest host-bit count whose usable addresses cover your requirement.
- Review the spare addresses. If the spare count looks thin, increase your host requirement and recalculate.
- Reset to plan another LAN. The Reset button clears the form for the next network.
Worked Example: 200 Hosts on 192.168.0.0
Suppose you are setting up an office network on 192.168.0.0 and you need addresses for 200 devices. Enter 192.168.0.0 and 200, then click Calculate.
The tool searches for the smallest number of host bits where 2 raised to that power minus 2 covers 200 hosts. Eight host bits give 254 usable addresses, which is enough, so the answer is a /24.
The calculator reports:
- Recommended CIDR: /24
- Subnet mask: 255.255.255.0
- Network address: 192.168.0.0
- Broadcast address: 192.168.0.255
- First usable IP: 192.168.0.1
- Last usable IP: 192.168.0.254
- Usable hosts: 254
- Spare addresses: 54
With 54 spare addresses beyond your 200 devices, the office has healthy room to grow without re-subnetting.
More Helpful Information
Counting hosts correctly
The number people forget most often is the infrastructure itself. A network with 180 user devices might also need addresses for the router, switches, wireless controllers, printers, and security cameras. Add at least 20 percent headroom so a hiring wave or a new device rollout does not force an emergency renumber.
Standard LAN sizes
Most small offices land on a /24 with 254 usable hosts because it is simple and generous. A busy department or a medium site might need a /23 with 510 usable hosts. Very large campuses use /22 or larger, but those are usually split into VLANs rather than one flat broadcast domain.
Private address space for LANs
LANs should always be built from private address space: 10.0.0.0/8 for large organizations with many sites, 172.16.0.0/12 for medium networks, or 192.168.0.0/16 for small offices. Public addresses belong on the internet edge, not on internal LANs.
Mistakes to avoid
The classic mistake is sizing for today’s device count with zero headroom, then discovering the subnet is full six months later. The other is going too big: a /16 for a 50-person office creates a giant broadcast domain for no benefit. Aim for the smallest subnet that covers your needs plus growth.
From one LAN to many
As organizations grow, one LAN becomes several: staff, guests, servers, voice, and management each get their own subnet and VLAN. Use this calculator for each segment separately, then allocate the subnets from your private address space without overlap.
Frequently Asked Questions
Q1: What is a LAN?
A: A local area network is a network confined to a small geographic area like an office, building, or campus, where devices typically share fast, low-latency connections.
Q2: How many hosts fit in a /24 network?
A: A /24 has 256 total addresses and 254 usable hosts after reserving the network and broadcast addresses.
Q3: How do I decide how many hosts I need?
A: Count every device requiring an address, including infrastructure like routers, switches, access points, and printers, then add 20 to 30 percent for growth.
Q4: What is a spare address?
A: A spare address is a usable host address left unassigned after your required devices are counted. Spares absorb future growth without renumbering.
Q5: Should I use public addresses on my LAN?
A: No. LANs should use private address ranges, with network address translation at the internet edge. Public addresses are scarce and must remain globally unique.
Q6: What is the difference between a /24 and a /23?
A: A /24 provides 254 usable hosts while a /23 provides 510. The /23 is exactly twice the size, useful when a single /24 is nearly full.
Q7: Can I change the subnet size later?
A: Yes, but it requires reconfiguring the mask on every device, router interface, DHCP scope, and firewall rule. Choosing correctly up front avoids that disruption.
Q8: What is a broadcast domain?
A: It is the set of devices that receive one another’s broadcast traffic. Each LAN subnet is a separate broadcast domain, divided by routers.
Q9: How many usable hosts does a /26 provide?
A: A /26 has 64 total addresses and 62 usable hosts, a popular size for small branch offices and departmental segments.
Q10: Should guests be on the same LAN as staff?
A: No. Put guest wireless on its own subnet and VLAN with firewall rules that block access to internal servers, so visitors cannot reach sensitive systems.
Q11: What gateway address should I use?
A: By convention, the first usable IP address, such as 192.168.0.1, is assigned to the router. Consistency makes documentation and troubleshooting easier.
Q12: How do VLANs relate to LAN sizing?
A: Each VLAN is typically its own subnet, so you size every VLAN separately with this calculator based on the hosts that VLAN will contain.
Q13: What if my host count falls between two subnet sizes?
A: Always round up to the larger subnet. Subnets come in powers of two, so a requirement of 300 hosts needs a /23 with 510 usable addresses.
Q14: Does a larger subnet slow down the network?
A: Slightly, because broadcast traffic reaches more hosts. Keeping subnets right-sized rather than enormous limits broadcast overhead.
Q15: Can this calculator plan a WAN link?
A: Yes. Enter 2 hosts for a traditional point-to-point link and it will recommend a /30, the standard size for links between two routers.
Conclusion
A well-planned LAN starts with the right subnet size, and the right size is simply the smallest block that covers your devices plus healthy growth. Enter your network address and host count above, take the recommended CIDR, and build a LAN with room to grow.