# /7 Subnet Mask (254.0.0.0) – Hosts, Range & FAQ

> The /7 subnet mask is 254.0.0.0. A /7 block holds 33,554,432 addresses with 33,554,430 usable hosts — ranges, wildcard, binary math and FAQs.

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# /7 Subnet Mask ReferenceIPv4

Two /8s side by side compose a /7: mask 254.0.0.0, 33,554,432 addresses. It is the widest prefix you will regularly see attached to realistic-looking public ranges in worked examples.

The /7 subnet mask is 254.0.0.0, equivalent to 1.255.255.255 as a wildcard. A /7 block contains 33,554,432 IP addresses (33,554,430 usable hosts).

## /7 facts at a glance

- **Subnet mask:** 254.0.0.0
- **Wildcard mask:** 1.255.255.255
- **Binary mask:** 11111110.00000000.00000000.00000000
- **Total addresses:** 33,554,432
- **Usable hosts:** 33,554,430 (excludes network & broadcast)
- **Block size:** 33,554,432 addresses (225)
- **Typical role:** Aggregation and supernetting

## Example /7 networks

A /7 spans a large share of the address space, so one aligned example says it all.

| Network | Usable range | Usable hosts |
| --- | --- | --- |
| 198.0.0.0/7 | 198.0.0.1 – 199.255.255.254 | 33,554,430 |

## How to calculate a /7 mask

A /7 mask sets the first 7 bits of a 32-bit number to 1 and leaves the remaining 25 bits as 0. In binary that reads `11111110.00000000.00000000.00000000`, which converts to dotted decimal `254.0.0.0`. Each block covers a contiguous run of 225 = 33,554,432 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving `1.255.255.255`.

## Where /7 is used

- Pairing exercises, such as 68.0.0.0/7 summarizing 68.0.0.0 through 69.255.255.255.
- Theory problems about summarizing adjacent classful-era blocks.
- Sanity checks that a candidate summary aligns on its bit boundary.

A /7 always begins on an even first octet. 205.0.0.0/7 is impossible; 204.0.0.0/7 is properly aligned and covers 204.0.0.0 through 205.255.255.255.

## Frequently asked questions

**What mask does /7 use?**

254.0.0.0, wildcard 1.255.255.255: seven one-bits and twenty-five host bits.

**How many addresses are in a /7?**

33,554,432 total and 33,554,430 usable by convention, which amounts to two complete /8s per block.

**Can a /7 start on an odd first octet?**

No. The seventh bit is the last fixed bit, so valid networks pair an even first octet with the odd one after it, like 206 together with 207.

## Open this block in a calculator

[Open the /7 block in the subnet calculator](https://itinsighthub.com/subnet-calculator/?q=198.0.0.0%2F7)

[Get the /7 wildcard mask →](https://itinsighthub.com/wildcard-mask-calculator/?q=%2F7)

### Related prefixes

[/6](https://itinsighthub.com/subnet/6/)[/8](https://itinsighthub.com/subnet/8/)[/24](https://itinsighthub.com/subnet/24/)[/26](https://itinsighthub.com/subnet/26/)[/28](https://itinsighthub.com/subnet/28/)[/30](https://itinsighthub.com/subnet/30/)

← /6 subnet mask
/8 subnet mask →

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