iPhone和iPad下各种常见控件的宽度和标准是一样的，所以这里就用iPhone说明。

 

Sizes of iPhone UI Elements

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Element Size (in points)
Window (including status bar) 320 x 480 pts
Status Bar
(How to hide the status bar)		 20 pts
View inside window
(visible status bar)		 320 x 460
Navigation Bar 44 pts
Nav Bar Image /
Toolbar Image		 up to 20 x 20 pts (transparent PNG)
Tab Bar 49 pts
Tab Bar Icon up to 30 x 30 pts (transparent PNGs)
Text Field 31 pts
Height of a view inside
a navigation bar		 416 pts
Height of a view inside
a tab bar		 411 pts
Height of a view inside
a navbar and a tab bar		 367 pts
Portrait Keyboard height 216 pts
Landscape Keyboard height 140 pts

Points vs. Pixels
The iPhone 4 introduced a high resolution display with twice the pixels of previous iPhones. However you don’t have to modify your  code to support high-res displays; the coordinate system goes by points rather than pixels, and the dimensi***** in points of the screen and all UI elements remain the same.
iOS 4 supports high resolution displays (like the iPhone 4 display) via the  scale property on UIScreen, UIView, UIImage, and CALayer classes. If the object is displaying high-res content, its scale property is set to 2.0. Otherwise it defaults to 1.0.
All you need to do to support high-res displays is to provide @2x versi***** of the images in your project. See the  checklist for updating to iOS4 or  Apple documentation for  Supporting High Resolution Screens for more info.
Adjusting Sizes
Click here to see how to adjust  View Frames and Bounds.
Additional References
Apple Documentation: Points vs. Pixels

Apple Documentation: UIBarButtonItem Class Reference says “Typically, the size of a toolbar and navigation bar image is 20 x 20 points.”

Apple Documentation: UITabBarItem Class Reference says “The size of an tab bar image is typically 30 x 30 points.”