SubnetPad

/20 Subnet Calculator

Results update as you type

A /20 block contains 4,096 addresses with 4,094 usable. This is the AWS default subnet size created in each availability zone when you use the VPC wizard.

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/20 = mask 255.255.240.0 • 4,094 usable addresses

Results for 192.168.16.0/20

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 /20 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 hosts4,096 total addresses in this subnet
More detailsNeighboring subnets, wildcard mask, hex, reverse DNS, and binary breakdown

Neighboring /20 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 address11000000.10101000.00010000.00000000
Subnet mask11111111.11111111.11110000.00000000
Network11000000.10101000.00010000.00000000
Broadcast11000000.10101000.00011111.11111111

Quick facts for /20

/20 reference guideBit split, overview, sizing tables, notable networks, and FAQ

Binary bit split

Network bits (20)Host bits (12)
Network bits
20
Host bits
12
Subnet mask
255.255.240.0
Wildcard mask
0.0.15.255
Total addresses
4,096
Usable hosts
4,094
Hosts formula
2^12 − 2
/24 relationship
16 × /24 networks

Overview

A /20 block contains 4,096 addresses with 4,094 usable. This is the AWS default subnet size created in each availability zone when you use the VPC wizard.

Common use cases

  • AWS default subnet per availability zone
  • Medium data center tier segment
  • Enterprise office site addressing
  • Azure subnet allocation

Subnet sizing reference

Divide /20 into…

PrefixSubnetsHosts each
/2122,046
/2241,022
/238510
/2416254

/20 fits inside…

SupernetHosts/20s inside
/198,1902
/1816,3824
/1732,7668
/1665,53416

Notable /20 networks

  • 192.168.16.0/20Example AWS default subnet range
  • 10.0.0.0/20Common cloud VPC subnet

Frequently asked questions

Common questions about /20 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