What is this, and who is it for?
This is a free IPv4 subnet calculator — no account, no ads, nothing to install. Type an address, and it works out the network details for you instantly. It's built for two kinds of people at once: total beginners who are still learning what a subnet even is, and working network engineers who need real VLSM design, Cisco/FortiGate config output, and multi-site addressing plans.
If you're new to subnetting
An IP address like 192.168.1.10 is split into two parts: a "network" part and a "host" part. The split point is set by the number after the slash — the /24 in 192.168.1.10/24. Everything before that split identifies which network you're on; everything after identifies which device on that network.
You don't need to memorize any of the math. Open the calculator, type an address, and hover any result label — a short explanation pops up for every term (network address, broadcast, subnet mask, and so on).
Quick start
- Go to the calculator and type any IPv4 address, e.g.
192.168.1.10.
- Drag the slider (or click a bit directly) to set how the address is split.
- Read the results below — hover any label for a plain-language explanation.
- Need more than one subnet? Scroll to VLSM Designer and enter how many devices each one needs.
Everything else on the page, in one glance
The calculator page has more sections than most people expect on first visit — here's what each one does, top to bottom:
- Cloud Subnet (AWS / Azure / GCP)
- Same address, but accounts for how each cloud provider reserves addresses per subnet — 5 for AWS/Azure, 4 for GCP — instead of the usual 2.
- Config Generator
- Turns the subnet above into real Cisco Router, Cisco Switch, or FortiGate CLI commands.
- VLSM Designer
- Enter how many hosts each subnet needs; it sizes and places each one with zero wasted addresses.
- Route Summarizer
- Paste several networks; get back the single smallest route that covers all of them.
- Network Audit
- Paste (or upload) an existing IP plan to check it for overlaps, duplicates, and unused gaps.
- Enterprise Design
- Model a whole organization — sites, then departments within each site — as one addressing plan.
- Topology Planner
- Connect those sites with WAN links: hub-and-spoke, point-to-point, or full/partial mesh.
- Save & Share / Export PDF
- Turn a finished design into a shareable link or a formatted document with a network diagram.
If you're a working network engineer
Past the basics, the tool covers real design work: multi-site enterprise addressing (sites → departments, auto-sized VLSM), AWS/Azure/GCP-aware cloud subnetting, WAN topology planning (hub-and-spoke, mesh, point-to-point), route summarization, an existing-plan audit for overlaps (paste or upload a CSV), and generated Cisco/FortiGate CLI — interface, ACL, NAT, DHCP, OSPF, VPN, and more. Every calculation runs on a real backend API, documented at /docs.html if you want to script against it directly.
Frequently asked
- Do I need to sign up or install anything?
- No. It's entirely browser-based and free — open the page and start typing.
- Is my data stored anywhere?
- Calculations aren't tied to you personally. If you use "Save & Share," that specific design is stored under a short code so the link works later — nothing else is tracked about you.
- Can I trust the generated Cisco/FortiGate commands?
- The syntax is correct and follows real vendor conventions, but always review any config — especially placeholder values like passwords — before applying it to a live device.
Open the calculator →