What’s the safe width for most clients?

The widely accepted safe width is 600 pixels. This width displays correctly in most desktop clients without horizontal scrolling, fits comfortably in preview panes, and scales well on mobile devices.

Why 600px? It's a legacy standard from when most email was viewed in desktop clients with preview panes around 700px wide. The 600px content area plus margins fits cleanly. Modern screens could support wider, but email client preview panes often haven't grown proportionally.

Safe doesn't mean optimal for everyone. Some brands successfully use 640-700px for desktop-heavy audiences. Mobile audiences don't care about the desktop width if the email is responsive. The 600px standard is a safe default-deviate only with data showing your audience and client distribution supports it. Test wider layouts thoroughly before deploying.