VLSM Calculator
Divide a network into variable-sized subnets based on host requirements. Optimizes IP allocation with largest-first strategy.
Try VLSM Calculator →What It Does
The VLSM (Variable Length Subnet Mask) Calculator takes a parent network block and a list of subnet requirements (each with a name and host count), then allocates optimally-sized subnets using the largest-first strategy. It minimizes wasted address space compared to fixed-size subnetting.How to Use It
- Navigate to IP Tools → VLSM Calculator from the top menu.
- Enter the parent network address and CIDR prefix (e.g., 192.168.1.0/24).
- For each subnet, enter a name and the number of hosts needed.
- Click Add Subnet to add more rows. Click the X to remove a row.
- Click Calculate VLSM.
- View the allocation table showing network, range, broadcast, mask, usable hosts, and wasted addresses for each subnet.
- Use Copy All or Download .txt to export the plan.
Presets
- Office (50, 20, 10, 5): Typical small office with 4 departments on a /24.
- Campus (200, 100, 50, 25, 10): Multi-building campus on a /22.
- Point-to-Point (2, 2, 2, 2): WAN links using /30 subnets from a /24.
Example: Office Network Design
You have 192.168.1.0/24 and need subnets for Engineering (50 hosts), Sales (20), Management (10), and Servers (5):
- Enter
192.168.1.0/24as the parent network. - Add 4 rows with the requirements above.
- Click Calculate.
The calculator allocates a /26 for Engineering, /27 for Sales, /28 for Management, and /29 for Servers — all fitting within the /24 with minimal waste.
Use Cases
- Network design: Plan IP allocation for a new office or campus.
- VLAN planning: Size subnets to match department or floor requirements.
- IP conservation: Maximize use of a limited address block.
- Documentation: Export the allocation table for network diagrams and change requests.
- Certification prep: Practice VLSM subnetting for CCNA/CCNP exams.