Work out dhcp pool size instantly with clear inputs, formula shown and shareable results.
A DHCP scope cannot exceed the usable addresses in its subnet minus the gateway, servers, printers and other statically assigned interfaces. Sizing then compares the remaining pool against the client count grown by a headroom factor, because guest devices, phones and short leases all inflate concurrent demand above the nominal seat count.
Pool sizing
usable = 2^(32-prefix) - 2; pool = usable - statics; needed = clients x (1 + growth); utilisation = needed / pool
Aim below about 80 percent. Above that, a burst of new devices or a stale lease backlog starts producing DHCP exhaustion and clients falling back to link-local addresses.
A reservation inside the pool range still occupies an address. Keeping statics in a block outside the pool makes the arithmetic and the audit trail cleaner.