SubnetPad

/25 Subnet Calculator

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A /25 block contains 128 addresses with 126 usable — exactly half a /24. It is commonly used to divide a standard /24 network into two equal halves, for example separating wired and wireless clients.

/1
/32

/25 = mask 255.255.255.128 • 126 usable addresses

Results for 192.168.1.0/25

Private (RFC 1918)Class C
Network addressThe first address — identifies the subnet itself
Broadcast addressThe last address — used to reach every device at once
Subnet maskSame as /25 in CIDR notation
First usable hostThe first IP you can assign to a device
Last usable hostThe last IP you can assign to a device
Usable hosts128 total addresses in this subnet
More detailsNeighboring subnets, wildcard mask, hex, reverse DNS, and binary breakdown

Neighboring /25 subnets

Wildcard mask
Used in Cisco ACLs and OSPF
CIDR notation
IP in hexadecimal
IP as 32-bit integer
Reverse DNS (PTR)
Host bits / subnet bits

Binary breakdown

IP address11000000.10101000.00000001.00000000
Subnet mask11111111.11111111.11111111.10000000
Network11000000.10101000.00000001.00000000
Broadcast11000000.10101000.00000001.01111111

Quick facts for /25

/25 reference guideBit split, overview, sizing tables, notable networks, and FAQ

Binary bit split

Network bits (25)Host bits (7)
Network bits
25
Host bits
7
Subnet mask
255.255.255.128
Wildcard mask
0.0.0.127
Total addresses
128
Usable hosts
126
Hosts formula
2^7 − 2
/24 relationship
2 fit per /24

Overview

A /25 block contains 128 addresses with 126 usable — exactly half a /24. It is commonly used to divide a standard /24 network into two equal halves, for example separating wired and wireless clients.

Common use cases

  • Split a /24 into two equal halves
  • Separate wired and wireless VLANs
  • Small office or department subnet
  • Cloud subnet with up to 126 hosts

Subnet sizing reference

Divide /25 into…

PrefixSubnetsHosts each
/26262
/27430
/28814
/29166

/25 fits inside…

SupernetHosts/25s inside
/242542
/235104
/221,0228
/212,04616

Notable /25 networks

  • 192.168.1.0/25Lower half of 192.168.1.x (.0–.127)
  • 192.168.1.128/25Upper half of 192.168.1.x (.128–.255)

Frequently asked questions

Common questions about /25 networks, subnet masks, and use cases.

All CIDR prefix sizes

/0/1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32