I buy, sell and collect antique dolls and am always looking for old replacement parts on eBay.  Even when sellers give exact measurements, it can be hard to know for sure if the part will fit with what you already have.  

Sometimes just knowing the measurement is enough but a lot of times you need to see the pieces together to see if the proportions and scale are just right.

I hit upon an easy way to know for sure what you’re getting.  All you need is the measurement of the part and your computer.

First, save the photo of the part to a folder on your computer.

Next, open MS Word and open a new document.  Pull down the INSERT menu at the top of the page, then click 'picture:  from file'.  Browse your folder for the photo you just saved and insert it into your Word document.

Now drag the corner of the photo in the document and resize until the part in the photo is exactly life size.  I simply hold a ruler against the screen to check this.  If the seller has included a ruler in the photo for sizing,

you can resize the photo until the ruler is perfectly scaled (1:1).

Once your photo is sized correctly on the monitor, simply hold the doll or parts that you have against the screen to see how it will look together!