How many addresses are in a /15 block?

A /15 block contains 131,072 total addresses (2^17) and 131,070 usable hosts.

What is the subnet mask for /15?

The subnet mask for /15 is 255.254.0.0 (binary: 11111111.11111110.00000000.00000000). The wildcard mask is 0.1.255.255.

How many /16 blocks fit inside a /15?

A /15 contains exactly 2 individual /16 networks.

How many /24 subnets fit in a /15?

A /15 block contains 2^9 = 512 individual /24 subnets.

How is /15 useful compared to /16?

A /15 is twice the size of a /16. It is useful when a single /16 (65K hosts) is not quite enough for a large site or region, but a full /14 (262K hosts) would be wasteful. Splitting a /14 into two /15s gives two equal large blocks.

/15 Subnet Calculator

Results update as you type

A /15 block contains 131,072 addresses. A common ISP allocation size and a useful boundary for splitting RFC 1918 ranges in enterprise environments.

Network size

/32

/15 = mask 255.254.0.0 • 131,070 usable addresses

Results for 10.0.0.0/15

Private (RFC 1918)Class A

Network addressThe first address — identifies the subnet itself

Broadcast addressThe last address — used to reach every device at once

Subnet maskSame as /15 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 hosts131,072 total addresses in this subnet

More detailsNeighboring subnets, wildcard mask, hex, reverse DNS, and binary breakdown

Neighboring /15 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 address00001010.00000000.00000000.00000000

Subnet mask11111111.11111110.00000000.00000000

Network00001010.00000000.00000000.00000000

Broadcast00001010.00000001.11111111.11111111

Quick facts for /15

Subnet mask: 255.254.0.0
Wildcard: 0.1.255.255
Usable hosts: 131,070
Total addresses: 131,072

/15 reference guideBit split, overview, sizing tables, notable networks, and FAQ

Binary bit split

11111111·11111110·00000000·00000000

Network bits (15)Host bits (17)

Network bits: 15
Host bits: 17
Subnet mask: 255.254.0.0
Wildcard mask: 0.1.255.255
Total addresses: 131,072
Usable hosts: 131,070
Hosts formula: 2^17 − 2
/24 relationship: 512 × /24 networks

Overview

A /15 block contains 131,072 addresses. A common ISP allocation size and a useful boundary for splitting RFC 1918 ranges in enterprise environments.

Common use cases

ISP address pool allocations
Large campus network address blocks
Enterprise country-level addressing

Subnet sizing reference

Divide /15 into…

Prefix	Subnets	Hosts each
/16	2	65,534
/17	4	32,766
/18	8	16,382
/19	16	8,190

/15 fits inside…

Supernet	Hosts	/15s inside
/14	262,142	2
/13	524,286	4
/12	1,048,574	8
/11	2,097,150	16

Frequently asked questions

Common questions about /15 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