blowing up an image for printing

is there a way one can tell what the max size an image can be blown up for printing? Meaning I have an image that looks fine for 8x10, but when I printed it at 11x14, it really looked bad... not as crisp as the 8x10.

or is this all trial & error?

any 4Mp image should go to 8x10 just fine. 6Mp will go much larger if it starts out clear and clean. I have gone to 20x30 with 6Mp 10D images many times.

The current 8Mp Canons will do that easily.

You'll be ok as long as you've got between 200~300 pixels per inch of print.
So, in your example, an image with 2000 pixels on the long side should give a good 10" long print, but the individual pixels may start to show at 14", when your density will have dropped to ~140 ppi.

Any current EOS will be OK for 14" at full frame. If not, look to your technique!

ok, thanks
some of the images I was thinking of printing are
https://photography-on-the.net/forum/showthre​ad.php?t=194078

You should be able to get a sharp 12X18" image from the 300D. I did it many times. Of course, if you're shooting medium jpegs, you should probably stick to the 8X10"s?
And... RAW rocks!

Some of the cheaper labs that I dont use for printing you can upload to them and it will tell you the max size the pic would look good at.
I think one was target.com


Sonya