PST to GMT

Enter a time in US Pacific Time and read it in Greenwich Mean Time. GMT is usually 8 hours ahead of PST.

Whether the gap holds all year

The gap is not the same all year: it ranges from 7 hours ahead to 8 hours ahead, because US Pacific Time and Greenwich Mean Time change their clocks on different dates. Those few weeks are when most calls are missed by an hour.

Which zones these letters mean

PST resolves to US Pacific Time and GMT to Greenwich Mean Time. Neither is ambiguous, so a time converted here means one thing only.

Questions

What does CST actually mean?

It depends who wrote it, and that is the problem. CST is US Central Time and it is also China Standard Time — fourteen hours apart. IST is India, Ireland and Israel. Every conversion page here names the zone it resolved an abbreviation to, rather than quietly picking one.

Why does the difference between two time zones change during the year?

Because countries change their clocks on different dates. The United States moves in March and November, the European Union in the last weekends of March and October, and the southern hemisphere moves the opposite way entirely. For a few weeks each year the usual gap is an hour out, which is when most mis-scheduled calls happen.