Let's pretend you open an image in Photoshop, and it has the following original image size:
To figure out the printable size of this image, you would first uncheck the "Resample Image" checkbox. Then, you would look at the value in the "Resolution" field. This image has a resolution of 600 PPI and we know that our target resolution for inkjet printing is 300 PPI. So, we are going to cut the resolution in half. If we halve the resolution, then Photoshop will double the document size. If you were to type "300" where it says "600," you would see that the Width and Height values automatically would double in value. The "Image Size" window would look like this:
Now you know the maximum document size you should print at (10x14). You would now click OK.