Hi,

If Single.TryParse(Lengthbox.Text, Length) AndAlso Single.TryParse(Width.Text, Width) _AndAlso Single.TryParse(Thicknessbox.Text, Thickness) AndAlso Single.TryParse(Ratebox.Text, Rate) Then
'Write your valid calculation code here
Length = Lengthbox.Text
Width = Widthbox.Text
Thickness = Thicknessbox.Text
Rate = Ratebox.Text
I managed to fix the code but I still dont know how to use:
If Single.TryParse(Lengthbox.Text, Length) AndAlso Single.TryParse(Width.Text, Width) _AndAlso Single.TryParse(Thicknessbox.Text, Thickness) AndAlso Single.TryParse(Ratebox.Text, Rate) Then
'Write your valid calculation code here
The first thing to do if there is something that you do not understand is to read the Documentation for the method that you are using. MSDN has a wealth of information on every Method and Property for Every Class and Type in VB.NET. Have a look here on the Single.TryParse method:-

http://msdn.microsoft.com/en-us/library/26sxas5t.aspx

Once you have read this you should be able to structure your code correctly.

With regards to rounding, have a look here:-

http://msdn.microsoft.com/en-gb/library/zy06z30k.aspx

Hope that helps.

Cheers,

Ian