How to size an exported image to a desired size when the total file is 11.5MB

[ARduckphotographer]

I'm attempting to send images to a lab for HDAcrylic prints. Can I assume that if the image is 11.5MB total size that I can export it in whatever size JPEG I desire as long as sufficient pixels are present? I typically use 300DPI. 

Thank you for responding. Clearly, I've a gap in my knowledge about sizing images. 

[JP Hess]

You cannot export a DPI setting from Lightroom. You can set a PPI (pixels per inch) setting, but it really doesn't have any impact on the quality of the image. If the image is 6000 x 4000 pixels that's its resolution. It doesn't matter what the PPI setting is. It has 6000 pixels of horizontal resolution, and 4000 pixels of vertical resolution. Changing the PPI setting isn't going to change that fact. You can change the PPI setting to anything you want, 72 or 300 or 600 or whatever. But it won't change the quality of the image or the print one little bit. A print, the same size, from an image set at 72 PPI, or 300 PPI, or 600 PPI, regardless of the size of the print, will render exactly the same quality. You have to decide how large of a print that many pixels will suitably produce. If you think it needs to be at 300 PPI, then divide 6000 x 300. That comes out to 20 inches. That will give you an idea of how large the image can be if you really think it needs to be printed at that high of a resolution.

[ARduckphotographer]

Jim

Thanks for responding.  I'm 80+ so I'm slow on the uptake. My Nikons have taken me all over North and South America, but I'm afraid I never bothered to learn aspect ratio.  I just cropped it according the "thirds" etc. DUH.

Example I have an image in LR that I'm about to export for printing. The image is 2953x2005 as a NEF. I have inserted those figures in the export image sizing block.  I'm hoping the exported JPEG will be 2953x2005 ppi.

Am I doing this correctly?  If the JPEG comes out that size, my lab can print it in the size I want.

Thanks again, I do appreciate being able to ask someone who knows and is willing to share their knowledge. 

[JP Hess]

If you think that image needs to be printed at 300 PPI, then the image with those pixel dimensions would support a printed image that measures 6 x 9". But the digital labs these days seem to be able to get more out of the images than that. I would order the print and see if you get a low resolution warning. Many of the online labs will warn you if you are ordering a print that is too large for the size of the file. I have printed images at 200 PPI that have produced satisfactory results. So it's just something you'll have to be the judge about.

[ManiacJoe]

Image quality is all about the number of pixels.

File size in MegaBytes does not matter.

The PPI/DPI field in the photo does not matter as this is the first number to be discarded and recalculated by the printing software. Calculating the PPI can help determine if you have enough pixels for the size you want. Most times these days a PPI of 150 or more will look fine for most purposes.