Hello Georges Nguyen,
About bar width calculation:
The factors that determine the bars' width are complex. Starting with the space - it depends on the space reserved for the RadChart itself, then the default view takes away some of the space for drawing series to show up some of its elements like the chart legend, title, axis, labels and ticks. After the place for the plotting area is determined the actual width of the bars is calculated. Remember, that if nothing else is specified, the RadChart will try to display all series items on the screen (using sampling with default threshold of 200). The width depends of the axis range, the number of major / minor ticks and the ticks distance. After all these factors are taken into account, the bar width percent reduces the bar size by a percentage of the determined size.
About categorical chart and bars width:
When you are using categorical axis you are using text instead of numbers. So setting the MinValue, MaxValue and Step doesn't make sense when using categories. You can try using the auto range, which will split the available size evenly for your bars. If you are not happy with the auto range you can try the using a numerical values with proper grouping. This approach is demonstrated in this
thread in our forum.
All the best,
the Telerik team
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