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Quick answer
What does the IP subnet planner calculate?
How many addresses and usable hosts fit an IPv4 prefix? This calculator uses cidr prefix length, and number of equal subnets to estimate ipv4 subnet capacity immediately in your browser.
With the values currently entered, the result is 254 — traditional usable hosts per subnet. It also shows addresses per subnet, subnet mask, total addresses requested, and cidr notation.
How to use the IP subnet planner
- Replace the example values with your own numbers.
- Review the result and supporting figures as they update automatically.
- Check the formula and assumptions before using the estimate for a decision.
Inputs used
- CIDR prefix length
- Number of equal subnets — entered in subnets
IP subnet planner formula
Addresses per subnet = 2^(32 − prefix); traditional usable hosts subtract network and broadcast addresses
Assumptions
- Every subnet uses the same IPv4 prefix.
- Traditional usable-host count reserves network and broadcast addresses; provider reservations may differ.
Practical guide
IP subnet planner example and edge cases
How many addresses and usable hosts fit an IPv4 prefix? Let's use a concrete example, then look at the assumptions that can move the answer.
Example: A practical ip subnet planner scenario
For this example, use cidr prefix length of 24, and number of equal subnets of 4 subnets. These are starting values, so replace them with numbers that match your situation.
- CIDR prefix length
- /24
- Number of equal subnets
- 4 subnets
Calculated result254traditional usable hosts per subnet
Start with traditional usable hosts per subnet. Then check addresses per subnet, subnet mask, total addresses requested, and cidr notation to understand what sits behind the main result.
Example results use the default display profile. The calculator above follows your selected country and units.
How to read the result
- Read the main result first. The supporting figures for addresses per subnet, subnet mask, total addresses requested, and cidr notation explain how the estimate is built.
- The method is Addresses per subnet = 2^(32 − prefix); traditional usable hosts subtract network and broadcast addresses. Keep the units consistent and use values from the same time period.
Edge cases worth checking
When cidr prefix length is unusual
Every subnet uses the same IPv4 prefix. Double-check this input before relying on the result.
When number of equal subnets is uncertain
Traditional usable-host count reserves network and broadcast addresses; provider reservations may differ. Run a lower and higher value to see a useful range.
What changes the result most
CIDR prefix length
Change cidr prefix length on its own first. This shows how strongly it affects the answer.
Number of equal subnets
Change number of equal subnets on its own first. This shows how strongly it affects the answer.
Try a different scenario
Small changes show whether the answer is stable or sensitive.
CIDR prefix length: 10% lower
221,022traditional usable hosts per subnet
CIDR prefix length: 10% higher
2662traditional usable hosts per subnet
Number of equal subnets: 10% higher
4 subnets254traditional usable hosts per subnet
Common mistakes
Check cidr prefix length
Every subnet uses the same IPv4 prefix. Make sure this matches the number you enter.
Keep number of equal subnets consistent
Traditional usable-host count reserves network and broadcast addresses; provider reservations may differ. Use the same units and time period throughout the calculation.
Do not rely on one ip subnet planner scenario
Run a cautious case and an optimistic case. The range is often more useful than one exact-looking number.
Use this result well
How many addresses and usable hosts fit an IPv4 prefix?
Real speed, compression, battery health, and device overhead can change the result.