The value ? A pixel doesn't have a "value".
What do you mean ?
Please see: https://www.mql5.com/en/docs/chart_operations/chartxytotimeprice
It is probably worth mentioning that there are 2 different ways to draw objects.
Sometimes it is necessary to mix these up e.g. you want to draw an object relative to time on the X axis, and pixels on the Y axis.
Under these circumstances, you will want to use ChartXYToTimePrice() or ChartTimePriceToXY() as Marco has suggested.