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IP Subnet Calculator

Use this IP subnet calculator to convert compatible units or encoded values for IP subnet.

Primary answer
CIDR block
Inputs to verify
IPv4 address, CIDR prefix length, and /31 interpretation
Use type
Use as an estimate that depends on assumptions.
Keyword intent
IP subnet calculator

Calculator

IP Subnet Calculator

Calculates cidr block from ipv4 address, cidr prefix length, /31 interpretation. Defaults are filled in so you can review a working example before changing inputs.

Enter four dotted-decimal octets, such as 192.168.1.10.

Enter a whole-number IPv4 prefix length from 0 through 32.

RFC 3021 treats both /31 addresses as usable host addresses on point-to-point links.

Result

Result reflects the current submitted inputs.

  • Risk B
  • Reviewed 2026-05-26
  • 2 sources
CIDR block192.168.1.0/24
Subnet mask255.255.255.0
Network address192.168.1.0
Usable host addresses254 addresses
First usable address192.168.1.1
Last usable address192.168.1.254
Broadcast address192.168.1.255
Wildcard mask0.0.0.255
Total addresses256 addresses

Breakdown

Input address
192.168.1.10
Prefix length
/24
/31 mode
RFC 3021 point-to-point
  • This packet supports IPv4 dotted-decimal addresses only.
  • Subnet masks are contiguous from the most significant bit, as expected for CIDR prefixes.
  • Standard subnets reserve the all-zero host value as the network address and the all-one host value as the directed broadcast address.
  • When RFC 3021 mode is selected for a /31, both addresses are treated as usable host addresses and no directed broadcast address is shown.
  • /32 is treated as a single-host route with one usable address.
  • Cloud-provider and vendor-specific reserved addresses are not subtracted.
  • Results are planning aids; validate behavior on the target router, firewall, operating system, or cloud platform.

Accuracy notes

Risk level
B
Reviewed
2026-05-26
Sources
2
Primary result
CIDR block

Formula logic is kept in a pure calculator module with fixtures, source notes, and page-visible assumptions.

Categories

What the result means

Use CIDR block as the headline answer for IP subnet. Network address and prefix length. Read the converted value first, then verify the source unit, target unit, and factor before reusing the number. Use subnet mask, network address, and usable host addresses to explain why CIDR block moved when an input changed. Keep the original value next to the converted value when using it in a workflow. Check source unit, target unit, dimension compatibility, exchange or conversion rate, and rounding precision before treating the result as final.

CIDR blockNetwork address and prefix length.
Subnet maskDotted-decimal subnet mask.
Network addressBitwise network address.
Usable host addressesUsable host count under the selected /31 mode.

Use the result this way

  1. Start with CIDR block, then use supporting outputs only to explain the primary answer.
  2. Verify ipv4 address, CIDR prefix length, and /31 interpretation before copying the result.
  3. Choose the mode or method first because it can change which formula is applied and stay within the documented minimum and maximum ranges.
  4. Keep the original value next to the converted value when using it in a workflow.

User job

How to use this calculator

Use IP Subnet Calculator when you need cidr block, then use subnet mask and network address to check the context for unit checks, engineering notes, recipes, travel, shopping, and measurement cleanup.

Best for

  • Converting compatible units
  • Auditing the factor used for a repeated conversion
  • Reviewing a default example before entering your own ipv4 address and cidr prefix length.

Check before relying

  • Make sure the source and target units measure the same kind of quantity.
  • This packet supports IPv4 dotted-decimal addresses only.
  • Subnet masks are contiguous from the most significant bit, as expected for CIDR prefixes.
  • Source context: RFC Editor / Internet Engineering Task Force, reviewed 2026-05-26.

Next useful step

  • Base64 Encode / DecodeUse next when the developer utility task needs output text instead of CIDR block.
  • Binary CalculatorUse next when the developer utility task needs decimal instead of CIDR block.
  • Hex CalculatorUse next when the developer utility task needs decimal instead of CIDR block.

Formula

IPv4 CIDR subnet facts are derived with unsigned 32-bit masks: network = ip & mask, broadcast = network | ~mask, and total addresses = 2^(32-prefix). Key assumptions: This packet supports IPv4 dotted-decimal addresses only. Subnet masks are contiguous from the most significant bit, as expected for CIDR prefixes. Standard subnets reserve the all-zero host value as the network address and the all-one host value as the directed broadcast address.

  • IPv4 CIDR subnet facts are derived with unsigned 32-bit masks: network = ip & mask, broadcast = network | ~mask, and total addresses = 2^(32-prefix).
  • This packet supports IPv4 dotted-decimal addresses only.
  • Subnet masks are contiguous from the most significant bit, as expected for CIDR prefixes.
  • Primary source context: RFC Editor / Internet Engineering Task Force.

Inputs

Enter ipv4 address, CIDR prefix length, and /31 interpretation for unit checks, engineering notes, recipes, travel, and measurement cleanup. Before calculating, choose the mode or method first because it can change which formula is applied and stay within the documented minimum and maximum ranges. IPv4 address: Enter four dotted-decimal octets, such as 192.168.1.10. CIDR prefix length: Enter a whole-number IPv4 prefix length from 0 through 32. /31 interpretation: RFC 3021 treats both /31 addresses as usable host addresses on point-to-point links.

IPv4 addressEnter four dotted-decimal octets, such as 192.168.1.10.
CIDR prefix lengthEnter a whole-number IPv4 prefix length from 0 through 32.
/31 interpretationRFC 3021 treats both /31 addresses as usable host addresses on point-to-point links.

Example

Using the default inputs, IP Subnet Calculator returns CIDR block of 192.168.1.0/24. Adjust ipv4 address, CIDR prefix length, and /31 interpretation to match your own scenario.

FAQ

How is CIDR block calculated here?

IPv4 CIDR subnet facts are derived with unsigned 32-bit masks: network = ip & mask, broadcast = network | ~mask, and total addresses = 2^(32-prefix). The first assumption to check is: This packet supports IPv4 dotted-decimal addresses only.

What does CIDR block mean for IP subnet?

Read the converted value first, then verify the source unit, target unit, and factor before reusing the number. Secondary values such as subnet mask, network address, and usable host addresses are there to explain the primary answer, not to replace it.

What should I enter for IPv4 address?

Enter four dotted-decimal octets, such as 192.168.1.10. Choose the mode or method first because it can change which formula is applied and stay within the documented minimum and maximum ranges.

How does CIDR prefix length change CIDR block?

Enter a whole-number IPv4 prefix length from 0 through 32. Changing it can alter CIDR block because the formula uses the submitted inputs together. Also compare source unit, target unit, dimension compatibility, exchange or conversion rate, and rounding precision.

Why does the IP subnet example show 192.168.1.0/24 for CIDR block?

The default inputs produce 192.168.1.0/24 for CIDR block. Treat that as a format and scale check, then replace every default value with your own inputs.

How do I avoid a IP subnet unit-direction mistake?

Keep the original value beside the converted value, confirm both units measure the same quantity, and check whether rounding is acceptable for the task.

Sources

Last reviewed: 2026-05-26

  • Reviewed 2026-05-26 · Source 2006-08
    RFC 4632: Classless Inter-domain Routing (CIDR)RFC Editor / Internet Engineering Task Force. CIDR prefix/mask model and classless IPv4 routing assumptions.
    Scope
    Best Current Practice document describing CIDR, prefix lengths, masks, and classless routing context.
    Supports
    CIDR prefix/mask model and classless IPv4 routing assumptions.
  • Reviewed 2026-05-26 · Source 2000-12
    RFC 3021: Using 31-Bit Prefixes on IPv4 Point-to-Point LinksRFC Editor / Internet Engineering Task Force. Rule that both addresses in a /31 prefix are interpreted as host addresses on point-to-point links and that directed broadcast is not used there.
    Scope
    Standards Track RFC defining /31 behavior for IPv4 point-to-point links.
    Supports
    Rule that both addresses in a /31 prefix are interpreted as host addresses on point-to-point links and that directed broadcast is not used there.

Disclaimer

This calculator is an educational estimate based on the inputs and assumptions shown on the page.