Subnet Split Calculator (Equal Subnets)
Divide a parent network into the number of equal subnets you need.
Your numbers
Your results
New prefix
New prefix
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New subnet mask
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Subnets available
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Usable hosts per subnet
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Subnet 1
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Subnet 2
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Last subnet
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Subnet Split Calculator (Equal Subnets) by TheCalcTools
How the Subnet Split Calculator (Equal Subnets) works
Enter the parent network address and prefix.
The number of extra bits is log₂ of the subnets needed, rounded up.
Each subnet gets a block of 2^(32 − new prefix) addresses.
The formula
New prefix = parent prefix + ceil(log₂ subnets)
Worked example
Using the default values shown in the calculator:
| Octet 1 | 10 |
|---|---|
| Octet 2 | 20 |
| Octet 3 | 0 |
| Octet 4 | 0 |
| Parent prefix (/n) | 16 |
| Subnets needed | 10 |
- 10 subnets need ceil(log₂ 10) = 4 extra bits, giving 16 subnets of /20.
- Subnet 1 is 10.20.0.0/20, subnet 2 is 10.20.16.0/20 and the last is 10.20.240.0/20.
Result:
| New prefix | /20 |
|---|---|
| New subnet mask | 255.255.240.0 |
| Subnets available | 16 |
| Usable hosts per subnet | 4,094 |
| Subnet 1 | 10.20.0.0/20 |
| Subnet 2 | 10.20.16.0/20 |
| Last subnet | 10.20.240.0/20 |
Frequently asked questions
Why do I get more subnets than I asked for?
Subnet counts are powers of two, so 10 subnets need 4 bits and give 16.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.