# /20 Subnet Mask (255.255.240.0) – Hosts, Range & FAQ

> The /20 subnet mask is 255.255.240.0. A /20 block holds 4,096 addresses with 4,094 usable hosts — ranges, wildcard, binary math and FAQs.

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# /20 Subnet Mask ReferenceIPv4

Sixteen /24s under 255.255.240.0: a /20 delivers 4,094 usable hosts, the sweet spot for a large office floor, a busy warehouse, or a cloud subnet that refuses to waste space.

The /20 subnet mask is 255.255.240.0, equivalent to 0.0.15.255 as a wildcard. A /20 block contains 4,096 IP addresses (4,094 usable hosts).

## /20 facts at a glance

- **Subnet mask:** 255.255.240.0
- **Wildcard mask:** 0.0.15.255
- **Binary mask:** 11111111.11111111.11110000.00000000
- **Total addresses:** 4,096
- **Usable hosts:** 4,094 (excludes network & broadcast)
- **Block size:** 4,096 addresses (212)
- **Typical role:** Mid-size networks and ISP allocations

## Example /20 networks

Three consecutive /20 blocks, starting at the /20 boundary that contains 198.51.100.0:

| Network | Usable range | Usable hosts |
| --- | --- | --- |
| 198.51.96.0/20 | 198.51.96.1 – 198.51.111.254 | 4,094 |
| 198.51.112.0/20 | 198.51.112.1 – 198.51.127.254 | 4,094 |
| 198.51.128.0/20 | 198.51.128.1 – 198.51.143.254 | 4,094 |

## How to calculate a /20 mask

A /20 mask sets the first 20 bits of a 32-bit number to 1 and leaves the remaining 12 bits as 0. In binary that reads `11111111.11111111.11110000.00000000`, which converts to dotted decimal `255.255.240.0`. Each block covers a contiguous run of 212 = 4,096 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving `0.0.15.255`.

## Where /20 is used

- One large-office production segment carrying thousands of endpoints.
- Cloud subnets sized with headroom for autoscaling fleets.
- Generous DHCP scopes where lease churn is high and exhaustion is unacceptable.

A /20 tiles sixteen times into a /16 and contains exactly sixteen /24s; its third octet advances in steps of 16.

## Frequently asked questions

**How many usable hosts are in a /20?**

4,094 of 4,096 total addresses; the network and broadcast slots account for the difference.

**What is the subnet mask for a /20?**

255.255.240.0, wildcard 0.0.15.255.

**How many /24s are in a /20?**

Sixteen consecutive ones, which is why a /20 is often described informally as sixteen class Cs.

**Is a /20 a good office size?**

For most large offices, yes: roughly four thousand devices with room to grow. Watch broadcast traffic and DHCP capacity if you flatten it into a single segment rather than VLAN-per-floor.

## Open this block in a calculator

[Open the /20 block in the subnet calculator](https://itinsighthub.com/subnet-calculator/?q=198.51.96.0%2F20)

[Get the /20 wildcard mask →](https://itinsighthub.com/wildcard-mask-calculator/?q=%2F20)

### Related prefixes

[/19](https://itinsighthub.com/subnet/19/)[/21](https://itinsighthub.com/subnet/21/)[/24](https://itinsighthub.com/subnet/24/)[/26](https://itinsighthub.com/subnet/26/)[/28](https://itinsighthub.com/subnet/28/)[/30](https://itinsighthub.com/subnet/30/)

← /19 subnet mask
/21 subnet mask →

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