Network

Subnet Calculator

Give the page an IPv4 address with a CIDR prefix and see the network and broadcast address, the usable host range, both subnet and wildcard masks, and a clear binary view. The same panel converts between prefix and mask, checks whether a target IP falls inside a subnet, and splits a network into smaller subnets by target prefix. Everything runs in the browser, so it fits cloud VPC planning, firewall reviews, and on-call troubleshooting.

  • CIDR calculation with network and broadcast addresses, usable host range, and total address count
  • Two-way conversion between prefix notation and dotted-decimal mask, plus a wildcard mask and binary view
  • IP containment check to verify whether a target address belongs to a given subnet
  • Subnet split by target prefix with start and end address for every resulting subnet
  • Address type detection for private ranges, loopback, link-local, multicast, and reserved addresses
tools/Subnet Calculator

Basic info

3 items
Input IP
192.168.1.10
CIDR
/24
Address type
Private range, 192.168.0.0/16

Address range

6 items
Network address
192.168.1.0
Broadcast address
192.168.1.255
First usable host
192.168.1.1
Last usable host
192.168.1.254
Total addresses
256
Usable hosts
254

Mask info

2 items
Subnet mask
255.255.255.0
Wildcard mask
0.0.0.255

Binary view

3 items
IP
11000000.10101000.00000001.00001010
Network address
11000000.10101000.00000001.00000000
Subnet mask
11111111.11111111.11111111.00000000

Overview

Brings the everyday IPv4 subnet tasks that usually require several utilities into a single workflow.

  1. 01

    Full CIDR calculation

    From an IPv4 address with CIDR, get the network and broadcast addresses, usable host range, total address count, and address type.

  2. 02

    Two-way mask and prefix conversion

    Switch between prefix notation and dotted-decimal mask while keeping the wildcard mask and binary view side by side.

  3. 03

    IP containment check

    Confirm whether a target IP falls inside a given subnet, useful for firewall rule audits, allowlists, and callback reviews.

  4. 04

    Split by target prefix

    Break a network down into smaller subnets by a target prefix and view the start and end of every resulting subnet.

  5. 05

    Address type detection

    Flag private ranges, loopback, link-local, multicast, and reserved blocks so reserved space does not get used by mistake.

  6. 06

    Local results, easy to share

    All calculations happen in the browser, and results are grouped into clean sections that paste straight into tickets and runbooks.

How to use

Pick a mode for the task at hand and the result panel updates as you type.

  1. 01

    Choose a mode at the bottom: Subnet calc, Mask convert, IP contains, or Subnet split.

  2. 02

    Fill in an IPv4 address with CIDR, a mask, a subnet, or a target prefix in the input panel.

  3. 03

    Use the common prefix shortcuts to avoid typing the same /24 or /26 over and over.

  4. 04

    Read the network range, mask info, binary view, or split list on the right.

  5. 05

    Copy the structured output and paste it into your ticket, change log, or planning doc.

Details

The same IPv4 input answers different questions depending on what you are working on, and this tool gathers those views together.

  • Network address, broadcast address, and usable host range are the starting point for most IPv4 planning
  • Wildcard mask is the bitwise inverse of the subnet mask and is convenient for writing router ACL entries
  • Binary view makes the boundary between network bits and host bits obvious during reviews and onboarding
  • IP containment paired with the subnet range helps double-check rules before applying a firewall change
  • Split by prefix gives the start and end address of every child subnet, useful for VPC and office network design
  • Address type detection separates private, loopback, link-local, and reserved space at a glance

Use cases

When address planning, access control, and service exposure need a shared source of truth, sort out the subnet boundaries first.

  1. Cloud VPC planning

    Lay out VPC subnets per workload, avoid overlap, and reserve room for growth before handing the plan to infrastructure.

  2. Office and datacenter networks

    Confirm subnet boundaries, broadcast addresses, and gateway positions so switches, APs, and DHCP stay aligned.

  3. Firewall and ACL review

    Check whether a source or destination IP matches the expected subnet to debug allow and deny rules.

  4. Callback allowlist verification

    Before going live, verify that partner or third-party callback IPs fall inside the agreed CIDR ranges.

  5. Training and onboarding

    Use the binary view and concrete ranges to explain how CIDR, masks, and host counts relate to each other.

  6. Pre-change rehearsal

    Simulate a subnet split before the real change, confirm the pool is large enough, then roll out in batches.

See also

When subnet math is part of a firewall or service-exposure review, keep Port Reference open to check protocols and ports. If a ticket only gives you an endpoint URL with an IP host, send it through URL Tools first to pull out the host, port, and path before deciding whether the address belongs to the intended CIDR range. To convert a single address between dotted decimal, integer, hexadecimal, and IPv6 forms, or to check what kind of address it is, open the IP Address Converter to see every form and its classification.

Best practices

Subnet results should sit next to the real network policy, otherwise the math is right but the config is wrong.

  • Sketch the full address pool before splitting, then decide how much room each segment should reserve.
  • Document gateway, reserved addresses, and DHCP pools explicitly to reduce conflicts.
  • Treat edge prefixes like /31 and /32 as special cases and confirm how usable hosts work for each.
  • Apply network changes in stages: validate, roll out in batches, then move to full coverage.
  • Use the same CIDR notation across docs and tickets to keep handoffs free of guesswork.
  • Include subnet calculation output in the pre-change checklist as evidence during review.

Limitations

This tool focuses on IPv4 subnet math and quick checks. It does not replace a full network simulator or a security policy review.

  • Vendor devices differ in how they treat reserved addresses or /31 semantics, so always check the device documentation.
  • Reachability between subnets still depends on routing, NAT, security groups, and firewall policy.
  • Malformed IPv4 or CIDR input produces explicit validation errors instead of guessed numbers.
  • Large address migrations should be staged with monitoring, rollback plans, and proper change windows.
  • Current scope is IPv4 only. IPv6 subnet workflows will be handled by a separate dedicated tool.
  • Correct subnet math does not guarantee end-to-end service reachability, which still needs integration testing.

FAQ

Common questions about how to use the tool, how the math works, edge cases, and how data is handled.

What does CIDR /24 mean?

The first 24 bits are network bits and the remaining 8 bits are host bits, which is the same as subnet mask 255.255.255.0 and gives a network of 256 addresses.

How many usable hosts does a /24 actually provide?

A /24 has 256 addresses in total. After removing the network address and the broadcast address, 254 are available for hosts in the usual case.

Why do /31 and /32 look different from other prefixes?

/31 is typically used for point-to-point links where both addresses can be assigned, and /32 represents a single-host route.

What is the difference between a subnet mask and a wildcard mask?

A wildcard mask is the bitwise inverse of a subnet mask. Routers use it in ACL syntax to express match ranges.

Why does an IP containment check fail?

Usually because the CIDR is typed wrong, the target IP is off by a digit, or the actual subnet does not match the one you expected.

Why does splitting require a longer target prefix?

Splitting creates smaller subnets, and smaller subnets need a longer prefix length than the source network.

Why is the subnet list capped at 1024 entries?

A larger list hurts readability and page performance. If you need a finer split, tighten the target prefix and plan in batches.

Does it support IPv6?

The current scope is IPv4 subnet workflows. IPv6 will be supported by a separate tool later.

Can it replace router configuration checks?

No. It calculates and verifies subnet boundaries quickly, but the final verification still needs to happen against the device configuration and routing policy.

Can I copy the result directly into a document?

Yes. The output is grouped into clean sections that paste into tickets, change records, and planning documents.

What is the binary view for?

It shows the boundary between network bits and host bits, which makes it easier to explain how masks and subnet splits work.

Is my input sent anywhere?

No. All calculations run in the current browser. The page does not send the IP or CIDR you enter to a server.

Related tools

For the next step in network work, the same toolset covers port lookup, URL inspection, and runtime browser capability checks.