This article describes how to set the height of a single-line
textbox control. The
TextBox control in C# (and VB.NET) ignores the height property and adjusts it to fit the font height. By calculating the exact font size needed, we can set the
TextBox to a desired height.
I had a C# project that required a single-line
textbox with adjustable height. I found many examples of how to adjust the width, but nothing on how to dynamically change the height of a
textbox. I did not want to use multi-line because I wanted to keep the auto-complete features of the single-line
Using the Code
textbox height is set by the size of the font, not the
TextBox.Height property. This makes it difficult if you are looking for an exact height. Luckily, the font property uses a float for the font size (
emSize). You can use fractions of fonts to fine-tune the
The calculation the
textbox uses to determine its height is:
Height = ( Font Size * Font Line Spacing / Font Em Height ) + 7
- Font Size - It is easiest to measure font size in pixels, so you do not have to factor in screen dpi.
- Font Line Spacing - The distance, in design units, between two consecutive lines of text.
- Font Em Height - Height, in design units of the font's widest letter - typically the letter M.
Textboxes have a 3-pixel lower and 4-pixel upper white space around the font height. Therefore, the calculation increases the height by 7 pixels.
We can reverse this calculation to obtain the font size needed for a desired height:
Font Size = ( height - 7 ) * Font Em Height / Font Line Spacing
This method will return a
font object that will set the size of your
private Font GetFontForTextBoxHeight(int TextBoxHeight, Font OriginalFont)
float desiredheight = (float)TextBoxHeight;
Font fnt = new Font(OriginalFont.FontFamily,
if (desiredheight < 8)
desiredheight = 8;
float FontEmSize = fnt.FontFamily.GetEmHeight(fnt.Style);
float FontLineSpacing = fnt.FontFamily.GetLineSpacing(fnt.Style);
float emSize = (desiredheight - 7) * FontEmSize / FontLineSpacing;
fnt = new Font(fnt.FontFamily, emSize, fnt.Style, GraphicsUnit.Pixel);
Whenever you have to set a
textbox size, set the
font property using the above method:
YourTextBox.Font = GetFontForTextBoxHeight(DesiredHeight, YourTextBox.Font);
Using the Control
Height Textbox is a user control that you can add to your form. It behaves the same as a regular
- You can set the height in the design view via the
- The control, if in single-line mode, will respond to docking and anchoring.
To use the control:
- Right-click on your toolbox in Design view.
- Click Browse. Navigate to AdjustableHeightTextbox.dll. Hit OK.
- Add the control to your form.
Points of Interest
- I learned that the .NET
TextBox code is basically a wrapper for the old MFC
textbox control. That is why it is not very customizable.
GetFontForTextBoxHeight() routine, with some tweaking, could be used for a
ComboBox control. The height calculations are close, but still off by a couple of pixels.
There is a lack of information on the inner workings of the
textbox control (as with most of the standard .NET controls). I hope this article has saved you hours of searching.
- 2008.09.07 - Posted original article
- 2008.09.10 - Added a user control version of the
textbox and a test project