I'm building a web application for a small office, to run their daily business. The employees will be logged in and working in the system thorugh the whole day.

My client is located in Israel, and I'm shopping for a hosting cloud provider for him to host the application that I'll build

My options is a server in the US, in Europe, and a local one - in Israel. A local provider is far more expensive.

I need to estimsate how much will the location of the server influence the reponsiveness of the system. And need to do it before I actually order the hosting, install the application and can measure it directly.

Is it a problem at all? Is the latency for a server located over the Atlantic generally felt by users and uncomfortable? How about from one side of Europe to another? (3000 Kilometers by air, from Germany to Israel)

Are there common numbers (like: average ping time between these two countries, or geographical regions, is such and such)

I don't have exact numbers to
Isreal but you can try speedtest.net/pingtest.net and see if you can find a server there for reference numbers. Ping from West coast to East Coast of US is ~100ms, from East Coast to Europe is another ~100ms. I have a friend who lives in Kuwait and usually gets 150-200ms ping to Europe, 250-300ms ping to west coast of US.

In terms of comfort none of these numbers should be exceeding half a second which means a two-way trip should generally be at worst 0.75-0.85 seconds, under good conditions probably 0.4-0.5s, possibly less from EU. Add to that whatever processing time your server has. Imo a server on East Coast of US or in Europe would be fine.