I am not into photography much but when I do have some nice photo's that I want to print, how do I make them the correct size so when I send them in to get printed, they don't crop them.
For example I have a photo, and I want a 4x6, or 5x7, what do I do with it to make it the correct measurements so it doesn't get cropped? Thanks

You need some information, such as the resolution.

To convert pixels to a printed or displayed image you need to know the number of pixels per inch (or cm if you are in a metrically inclined country). This is abbreviated ppi, also called dpi for dots per inch, and represents the resolution of the image.

A typical display like your computer screen is about 72ppi. So to display a four inch image on the screen you will want at least 6" x 72ppi = 432pixels wide and 4" x 72ppi = 288pixels high. In practice most devices can scale an image down for display and it will look fine so those numbers become minimums. Anything less than that can be expanded to fill four inches but it will look pixelated.

For a printed image you want a much better resolution as printers can print much finer detail and the human eye can pick out that detail. Usually for a printed image you need around 300ppi for the minimum resolution. So now your 4"x6" print will require 6" x 300ppi = 1800pixels wide and 4" x 300ppi = 1200pixels high. Again these are minimum numbers as a larger image can be scaled down by the printing software.

So make sure your image is at least 1800 x 1200 pixels and it should print a 4" x 6" image very nicely.

Ok, these are the photo properties of the pic I sent to Walmart-Kodak lab and they had to crop a bit off the bottom which spoiled it. I want it to fit in a 5x7 frame and it being cropped, it did't fit.

Your image is the wrong shape to exactly fit 5x7

If it's 2556 pixels on the long (7) side then the short side will have to be (2556 / 7) * 5 = 1825.7 pixels long.

So you will have to add extra pixels to your image to make it fit exactly.

The lab are scaling your image to fill the paper, so making 1804 pixels fit 5 inches, you're only going to get (1804 /5 ) * 7 = 2525.6 pixels on the long side.

In the end you will either have to add extra pixels, or crop it yourself to the 5x7 aspect ratio.

Of course we can then get into the questions about how you are going to mount the photo for display - is it going into a frame which has a matte? if so what is the size/shape of the aperture in the matte?

Kevin

Kevin is correct.
You will need to crop or scale your photo to fit. So if you have a dip of say 300pip you multiply 5 and 7 by 300 to get the pixel size of 300pip/dip. Or a dip of 72pip would mean you would need to multiply 5 and 7 by 72 to get the pixel size for that resolution.

I might have known I would have to do math... UGH

It's only simple multiplication.
You need to know what resolution the photos are at. To be able to make them the correct size, so that they won't get chopped off when they resize them.

No maths required...

Use the Image>>Canvas Size to enlarge the canvas to 120%

Set the crop tool use use a fixed aspect ratio of 5:7

Drag the crop rectangle around to see where you need to add stuff, or crop stuff:


Kevin

They get cropped because they haven't got the same aspect ratio (width/height) as the paper. To create an image with the right aspect ratio, use the Crop tool, and in the Tool options set the "Fixed" selector to "Aspect ratio" and the entry field under it to W:H (for instance 7:5 for landscape orientation on 5x7 paper). Then when you use the tool the crop rectangle is constrained to the set aspect ratio.

Of course, the picture is cropped, but at least you picked the part to keep. You can also increase the canvas size (with your picture centered), and do the same, the difference being that this will add space where necessary. Then export to JPG (this will add a default background to fill the transparency).

You can one day send a test image with markers going to the edges (thin one-pixel diagonal lines intersecting on the edges). You can then tell if they crop more that what is required by the aspect ratio conformance: