IP address planning calculator
Size the block for what the network will be, not for what it is today. Renumbering later is painful.
%
%
Prefix length to allocate
23
- Addresses needed
- 266
- Usable addresses in that prefix
- 510
- Spare addresses
- 244
- Headroom factor
- 1.917
- Projected devices
- 241
Show the working
- Devices today = 120
- Annual growth = 15
- Years to plan for = 5
- Infrastructure reserve = 10
- Projected devices = 120 * (1 + 15/100)^5 = 241.363
- with_reserve = 241.363 * (1 + 10/100) = 265.499
- Addresses needed = ceil(265.499) = 266
- bits = ceil(log2(266 + 2)) = 9
- Prefix length to allocate = clamp(32 - 9, 0, 32) = 23
- Usable addresses in that prefix = 2^9 - 2 = 510
- Spare addresses = 510 - 266 = 244
- Headroom factor = 266 > 0 ? 510 / 266 : 0 = 1.917 29
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
Scenarios & local history
Compare a saved scenario
Recent calculations
The formula
- projected devices = today x (1 + growth)^years
- prefix = 32 - ceil(log2(addresses + 2))