Normal Distribution Calculator
This graphical calculator computes the probabilities of a normal distribution falling in a given range. The range is determined by dragging out a shaded area under the graph of a normal curve.


  1. Click in one of the dark gray margins at either side of the graph to bring up a "guide line" which you can drag out across the graph. A shaded area is marked out behind the guide, and the window displays the probability of the distribution falling in this area.
  2. You can draw out a second guide, to mark out two-sided regions.
  3. Click and drag to move the guide lines once you have laid them out. Drop a line back in the gray margin area to remove it from the screen.
  4. The graph of the normal distribution is shown for values of x between xMax and xMin, which can be changed by typing in the textboxes.
  5. Initially, figures are given for a distribution with mean 0 and standard deviation 1. You can changes these values by typing in the appropriate boxes.
  6. You can enter numerical values for the guide positions by clicking the "Set range..." button. Enter the values of the probability range in the fields of the pop-up panel, and click the OK button (the green check) or dismiss the panel with the Cancel button (the red cross).