unit-vw
CSS property · 17 supported, 0 partial, 3 unsupported across 21 clients
17 of 21 email clients render unit-vw fully (Sep 2, 2026 data); it breaks outright in Outlook (New), Outlook Classic, Fastmail.
- 6/7 webmail, 3/6 desktop, 8/8 mobile clients support unit-vw fully.
- Unsupported in Outlook (New), Outlook Classic, Fastmail.
- Outlook Classic (Word engine, supported to at least 2029) does not fully support unit-vw, and its replacement changes little here; see the deprecation diff.
- Across all clients, only 6 of 298 tracked HTML/CSS features render identically everywhere.
Source: caniemail.com (MIT), via the Emailens engine. Last tested upstream Feb 25, 2020, synced by Emailens Sep 2, 2026.
Client Support
| Client | Category | Engine | Support |
|---|---|---|---|
| Gmail | webmail | Gmail Web | SupportedSee caveat 1 |
| Gmail Android | mobile | Gmail Mobile | Supported |
| Gmail iOS | mobile | Gmail Mobile | Supported |
| Outlook 365 | webmail | Outlook Web | SupportedSee caveat 1 |
| Outlook (New) | desktop | Outlook Web | Unsupported |
| Outlook Classic | desktop | Microsoft Word | Unsupported |
| Outlook iOS | mobile | Outlook Mobile | Supported |
| Outlook Android | mobile | Outlook Mobile | Supported |
| Outlook for Mac | desktop | WebKit | Supported |
| Apple Mail | desktop | WebKit | Supported |
| Apple Mail iOS | mobile | WebKit | Supported |
| Yahoo Mail | webmail | Yahoo | SupportedSee caveat 1 |
| Yahoo Mail Android | mobile | Yahoo | Supported |
| Yahoo Mail iOS | mobile | Yahoo | Supported |
| Samsung Mail | mobile | Samsung | Supported |
| Thunderbird | desktop | Gecko | Supported |
| HEY Mail | webmail | WebKit | Supported |
| Proton Mail | webmail | Proton | Supported |
| AOL Mail | webmail | AOL | SupportedSee caveat 1 |
| Fastmail | webmail | Fastmail | Unsupported |
| Superhuman | desktop | Blink | Unknown |
Documented caveats (1)
- 1.Gmail, Outlook 365, Yahoo Mail, AOL Mail: The HTML of the email message is embedded directly on the webmail (not in an <iframe>) and may not fill the full viewport's width. In this case, the vw values are relevant to the viewport (browser window) not the email message.
Caveats recorded by caniemail.com (MIT) and carried verbatim, one entry per wording rather than per client.
Client-by-client behaviour for unit-vw
Fully supports unit-vw (17): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook iOS, Outlook Android, Outlook for Mac, Apple Mail, Apple Mail iOS, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Samsung Mail, Thunderbird, HEY Mail, Proton Mail, AOL Mail.
No support (3): Outlook (New), Outlook Classic, Fastmail. Plan fallbacks for these clients before relying on unit-vw in production sends.
Behaviour unverified in: Superhuman.
Fixes & Workarounds
Outlook (New)
Unsupported"unit-vw" is not supported in this email client.
Outlook Classic
Unsupported"unit-vw" is not supported in this email client.
Fastmail
Unsupported"unit-vw" is not supported in this email client.
Related Features
Check your own HTML for unit-vw
Paste your own, or run the sample below. Analyzed in this page, with no signup and nothing stored.
Test your unit-vw layout across 21 email clients
Preview rendering, catch CSS issues, and see how unit-vw displays across Outlook, Gmail, and Apple Mail. Free, no account needed.
Instant live preview · No signup required · 21 email engines
Last tested upstream: · Last synced by Emailens:
caniemail.com (MIT) records Feb 25, 2020 as the last time unit-vw was tested in a real client, 6 years before this sync. Syncing copies that result forward, it does not re-test it. Carried in @emailens/engine data v0.12.2.