# /3 Subnet Mask (224.0.0.0) – Hosts, Range & FAQ

> The /3 subnet mask is 224.0.0.0. A /3 block holds 536,870,912 addresses with 536,870,910 usable hosts — ranges, wildcard, binary math and FAQs.

- Page URL: https://itinsighthub.com/subnet/3/
- Markdown variant of this page: append `?format=md` to any URL on this site or send `Accept: text/markdown`.
- Full site index for AI assistants: https://itinsighthub.com/llms.txt
- Full site export: https://itinsighthub.com/llms-full.txt

# /3 Subnet Mask ReferenceIPv4

With mask 224.0.0.0, a /3 locks three bits and captures the entire top eighth of IPv4: 536,870,912 addresses. That region is deliberately special-purpose, holding multicast plus the reserved experimental range.

The /3 subnet mask is 224.0.0.0, equivalent to 31.255.255.255 as a wildcard. A /3 block contains 536,870,912 IP addresses (536,870,910 usable hosts).

## /3 facts at a glance

- **Subnet mask:** 224.0.0.0
- **Wildcard mask:** 31.255.255.255
- **Binary mask:** 11100000.00000000.00000000.00000000
- **Total addresses:** 536,870,912
- **Usable hosts:** 536,870,910 (excludes network & broadcast)
- **Block size:** 536,870,912 addresses (229)
- **Typical role:** Aggregation and supernetting

## Example /3 networks

A /3 spans a large share of the address space, so one aligned example says it all.

| Network | Usable range | Usable hosts |
| --- | --- | --- |
| 192.0.0.0/3 | 192.0.0.1 – 223.255.255.254 | 536,870,910 |

## How to calculate a /3 mask

A /3 mask sets the first 3 bits of a 32-bit number to 1 and leaves the remaining 29 bits as 0. In binary that reads `11100000.00000000.00000000.00000000`, which converts to dotted decimal `224.0.0.0`. Each block covers a contiguous run of 229 = 536,870,912 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving `31.255.255.255`.

## Where /3 is used

- Explaining where multicast and experimental addressing live.
- Reserved-space accounting when auditing how much of IPv4 is actually assignable.
- Advanced CIDR drills on high-order bit boundaries.

224.0.0.0/3 decomposes into multicast 224.0.0.0/4 (RFC 1112) plus reserved 240.0.0.0/4. Neither half is public unicast space, so the block never appears as an allocation.

## Frequently asked questions

**How many addresses are in a /3?**

536,870,912 total; the calculator convention yields 536,870,910 usable, although in reality this slice of space is not host-addressable at all.

**Which mask belongs to /3?**

224.0.0.0, with wildcard 31.255.255.255: three fixed one-bits and twenty-nine host bits.

**Can hosts use addresses from 224.0.0.0/3?**

No. The range 224.0.0.0 through 255.255.255.255 is multicast (RFC 1112) plus reserved space, so ordinary interfaces never take an address from it.

## Open this block in a calculator

[Open the /3 block in the subnet calculator](https://itinsighthub.com/subnet-calculator/?q=192.0.0.0%2F3)

[Get the /3 wildcard mask →](https://itinsighthub.com/wildcard-mask-calculator/?q=%2F3)

### Related prefixes

[/2](https://itinsighthub.com/subnet/2/)[/4](https://itinsighthub.com/subnet/4/)[/24](https://itinsighthub.com/subnet/24/)[/26](https://itinsighthub.com/subnet/26/)[/28](https://itinsighthub.com/subnet/28/)[/30](https://itinsighthub.com/subnet/30/)

← /2 subnet mask
/4 subnet mask →

---

© 2026 ITInsightHub · [About](https://itinsighthub.com/about/) · [Contact](https://itinsighthub.com/contact/) · [Privacy](https://itinsighthub.com/privacy/)