You can specify `ImageSize` in inches. From [docs > ImageSize> MoreInformation](http://reference.wolfram.com/mathematica/ref/ImageSize.html):

>      Specifications for both width and height can be any of the following: 
>          ...
>          72di	        di inches (before magnification)
>          ... 

Examples:
 
    Row[{Plot[{Sin[x], Cos[x]}, {x, -2 Pi, 2 Pi}, Frame -> True, 
    AspectRatio -> 1/GoldenRatio, ImageSize -> 72 2], 
    Plot[{Sin[x], Cos[x]}, {x, -2 Pi, 2 Pi}, Frame -> True, 
    AspectRatio -> 1/GoldenRatio, ImageSize -> 72 3], 
    Plot[{Sin[x], Cos[x]}, {x, -2 Pi, 2 Pi}, Frame -> True, 
    AspectRatio -> 1/GoldenRatio, ImageSize -> 72 5]}]

![enter image description here][1]


  [1]: https://i.sstatic.net/OdZP3.png