VLSM Subnet Calculator
Plans a network where each subnet gets only the addresses it needs.
Addresses allocated
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Addresses left —
Subnets, largest first
Reading this —
The formula
subnet size = smallest 2^n ≥ hosts + 2
Subnets are placed largest first. Since each size is a multiple of every smaller one, they line up with no gaps.
What to watch out for
Leave room for growth when you enter host counts, since resizing a subnet later usually means renumbering.
Frequently Asked Questions
How big a subnet do 60 hosts need?
A /26, which has 62 usable addresses.
What does VLSM stand for?
Variable-length subnet masking: subnets of one network can have different mask lengths, rather than all being the same size.