FLSM Calculator
Divide a network address into equal-sized subnets for consistent addressing policies.
Enter network details to divide into equal subnets.
What this tool does
The Fixed Length Subnet Mask (FLSM) calculator divides a network address into multiple subnets of equal size. Unlike VLSM, which allows for variable sizing, FLSM enforces a consistent subnet mask across all segments. This tool calculates the necessary mask and resulting subnets based on either a target subnet count or a specific target mask.
When engineers use this
- Designing standardized addressing schemes for branch offices (e.g., assigning a /24 to every site).
- Allocating point-to-point links in bulk (e.g., carving a /24 into 64 /30s).
- Planning network segmentation where all VLANs require the same host capacity.
How to interpret the results
- Bits Borrowed: The number of host bits converted to network bits to create the subnets.
- Total Subnets: The maximum number of subnets created with the new mask.
- Hosts: The number of usable IP addresses per subnet.