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IP Range CalculatorPRO
IPv4 Subnetting & RangeInstant Client-Side Tool

Prefix to Host Capacity Calculator

Calculate capacity for a specified prefix.

Prefix to Host Capacity Calculator: inputs and results

Enter an IP address, CIDR prefix, or range. Then check its first and last address below.

Quick presets:

Calculated Boundaries & ParametersReady

Network Address192.168.1.0
Broadcast Address192.168.1.255
First Usable Host192.168.1.1
Last Usable Host192.168.1.254
Subnet Mask255.255.255.0
Wildcard Mask0.0.0.255
Total Addresses256
Usable Host Range254

Key Capabilities

  • •100% Client-Side: Zero telemetry or server latency.
  • •RFC Compliant: Exact 32-bit and 128-bit integer precision.
  • •Quick Copy: Instant access to CIDR, mask, and range bounds.
  • •Cross-Platform: Works on desktop, tablet, and mobile browsers.
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Network Address Calculator

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IPv4 Broadcast Address Calculator

Find broadcast addresses where applicable.

First and Last Address Calculator

Identify a range’s endpoints.

Usable IPv4 Host Range Calculator

Apply the selected subnet-use rules.

How Prefix to Host Capacity Calculator Works?

This tool works by converting a prefix length into the number of usable hosts, then applying a planned fill target to show the practical device capacity.

  1. Enter a prefix

    Type a prefix such as /23.

  2. Compute usable hosts

    2^(32 − 23) − 2 = 510 usable hosts.

  3. Apply a fill target

    Many teams plan to 80 % utilization. 510 × 0.8 = 408 devices.

  4. Show subnets per parent

    The calculator shows how many /23 subnets fit in a /16 parent: 2^(23 − 16) = 128.

Prefix to Host Capacity Calculator Formula

The formula is Capacity = 2^(32 − p) − 2, and the planned capacity equals Capacity × Fill Target.

Usable capacity

C = 2^(32−p) − 2

Standard subnets from /0 to /30.

Planned capacity

C_plan = floor(C × F)

F is the fill target, for example 0.8.

Subnets per /16

S = 2^(p − 16)

Valid for prefixes /16 to /32.

Hosts per /16

S × C

The total device capacity of a /16 carved into prefix p.

Worked example: /23 at an 80 % fill target

Capacity    = 2^9 − 2 = 510 hosts
Planned     = floor(510 × 0.8) = 408 hosts
Per /16     = 2^(23−16) = 128 subnets
Hosts / /16 = 128 × 510 = 65,280 hosts

Prefix to Host Capacity Calculator Conversion Table

The table lists usable capacity, planned capacity at 80 %, and subnets per /16 for 13 prefixes.

PrefixSubnet MaskUsable HostsPlanned at 80 %Subnets per /16
/16255.255.0.065,53452,4271
/17255.255.128.032,76626,2122
/18255.255.192.016,38213,1054
/19255.255.224.08,1906,5528
/20255.255.240.04,0943,27516
/21255.255.248.02,0461,63632
/22255.255.252.01,02281764
/23255.255.254.0510408128
/24255.255.255.0254203256
/25255.255.255.128126100512
/26255.255.255.19262491,024
/27255.255.255.22430242,048
/28255.255.255.24014114,096

What is Prefix to Host Capacity Calculator?

The Prefix to Host Capacity Calculator is a tool that returns how many devices an IPv4 prefix supports, both at full capacity and at a planned utilization target.

Full capacity counts every usable host. Planned capacity leaves room for growth, DHCP lease overlap, and temporary devices. A /24 has 254 usable hosts and 203 planned hosts at 80 %.

The calculator works in the opposite direction of the Host Requirement to Prefix Calculator. Engineers start with a prefix they already own and read off how many devices fit inside it.

What are the uses of Prefix to Host Capacity Calculator?

There are 5 main uses of the Prefix to Host Capacity Calculator, including site capacity checks, DHCP planning, and procurement.

  • Checking existing subnets

    A /25 with 110 devices runs at 87 % of 126 hosts. The calculator flags subnets above the fill target.

  • Planning DHCP lease headroom

    Short DHCP leases and roaming clients need spare addresses. The planned value reserves 20 % of the pool.

  • Carving a parent block

    A /16 split into /22 subnets gives 64 subnets of 1,022 hosts each.

  • Estimating site capacity

    Branch offices with a /24 support about 200 devices at 80 % fill.

  • Supporting procurement decisions

    Teams compare the device capacity of a /22 and a /21 before buying or requesting address space.