First, I think you mean 10MP, not MB. Megabyte is file size on a hard drive or memory card, it's not the same as pixels contained within it.

If you want a 20X24 print at 300ppi, that would be about 44MP of data required to achieve that goal. But I can tell you for a fact that it's not necessary to have that much resolution. You don't have a camera with a sensor that has that resolution anyway. I have made exceptionally nice 13X19 prints at 300ppi with an 8MP file even after cropping about 25% of the picture away, which probably brought the total pixel count down to about 6MP. That would mean that a 10MP or 12MP file would make a great 20X24. Be aware you may get some opinion here that you can make a wall sized poster for a train station with a 5MP file but those are viewed from 30 or 40 feet away.

Prints also don't have to have 300ppi to be excellent. Most home printers (but I assume you're sending these out) only require between 180ppi and 240ppi to give you prints that are as good as Kodak and Fuji machines at discount stores and drug stores. So a 20X24 printed at 180ppi would be 15.5MP or at 240ppi it would be 27.65MP. Still awfully high MP files for the common person's camera.

But that's assuming you would want and need the same pixels per inch at 20X24 as you would at 4X6. It has been said on here by many, and I'd have to agree with the concept to some extent, that pixel count for bigger enlargements don't have to be as high as small handheld prints because they won't be viewed at close range so a lower pixel count is acceptable. So try having one print made with a 10MP to 12MP file and see what happens.

Be aware that any out-of-focus areas of the photo that may not even be noticeable on small prints are going to be greatly enhanced and very noticeable on a 20X24, so don't be surprised by it. You'll want to blame it on low resolution but it is more likely to be focus blur that you didn't see before. Try looking at your photo file full screen on a 24" class LCD monitor before having it printed and you'll see what I mean.

There is also "interpolation software" available that does magic to a photo file by effectively doubling the pixels for printing purposes. A simple explanation is that the software carefully clones existing pixels and fills the holes between pixels with the clones for enlargement purposes. This gives the effect of doubling the MP of your file but it actually isn't doubled with real pixels, they're fake ones - but very good fake ones. This means an 8MP file becomes similar to a 16MP file when it prints and the results are astounding.

I was told by a regional training supervisor of Olan Mills that they use older Olympus 5MP cameras for their studio shooting. The Olan Mills processing lab must be using interpolation software before printing because they can do a 36X48 or anything you want from the 5MP file and the print quality will knock your socks off (of course, the price then blows your wallet across the room too).

Hope that helps.

Nope, not MP, when you right click on a photo go down to properties, then click on the details tab, scroll down to file and under file size it says the photo is 10.2 (MB)...

What are you using when you click on the photo? Windows Explorer? Editing software?

Your camera is unlikely to create files larger than 4.5 to 5MB if you're shooting in JPG although they would be much larger if you shoot in RAW.

In either case, the MB that the file requires for saving it has nothing to do with the quality of what's inside the file. Pixel count in MP is the key to whether the file will make a good clean enlargement.