How to calculate the amount of data used when logging?

ANSWER 

The log depends on following parameters:

• on how many log parameters there are
• on the format, number of digits for every parameter (number of decimals etc.)
• on the sample time

If there is a case where the log parameters are five digits and the comma to separate the values it will give 6 byte per log parameter. Every row holds the date and time, which give additional 16 bytes per row.

So roughly the following calculation can be done:

DateTime + (number of log parameters * byte per log parameter) => 16 + ( x * 6 ) This number of bytes will be stored for every sample.

The parameter names shall be added, which counts 1 byte per character + 1 (ex, parameter1 will give 11 bytes), that is stored once for a log file.

Examples:
16 integer parameter every 10 minutes: 16 + (16 * 6) = 112 bytes per sample > around 16kB/day or 480Kb/month.

16 floating point parameter every 10 minutes: 16 + (16 * 16) = 272 bytes per sample > around 40kB/day or 1.1Mb/month

This estimate is only for the logged data, if you access the real time values each refresh will generate some traffic as well, if you count every character that is shown in the Value fields and double that then it will be close to the generated traffic for each refresh.