If I understand correctly you are talking about the Item Labels and not the Axis Labels.
This is known problem in the RadChart - when the height is not enough, the labels do not have enough space and they get clipped. This is not the result of the number of the items by itself, but because of the number of items - the space is not enough and the labels get clipped.
While you cannot simply fix this, I can make several suggestions:
1. Turn off intelligent labels.
2. Change the LayoutMode of the AxisX to Inside:
.radChart.DefaultView.ChartArea.AxisX.LayoutMode = AxisLayoutMode.Inside;
3. Increase the height of the chart so that there is enough space for all labels.
4. Do not show any labels. Show tooltips instead.
5. Decrease the font size of the textbox in the ItemLabel (see how in this help topic
Let us know if these suggestions (or a combination of them) help you.
the Telerik team
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