What size should I make my file?

I'm designing a 12" x 48" sign/flyer that showcases some of the sports products that we have available. Once designed, we're going to print it through our lab.

I'm having trouble deciding what size I should make the finished file, as I know a full 12" x 48" file in Photoshop would be a nightmare to work on and save. I'm planning on doing it at 300dpi, but I'm wondering if designing it at 50% or 25% of final size would still yield a decent enough print. We don't need it to be crystal clear, but I don't want to lose so much quality that it looks bad. Any thoughts?

Any help is appreciated! Thanks!

One thing you can clear up: is this image going to be a composite/combination of shots or a single image?

If a single image, well, you certainly don't want to downsize the file! At 12x48 you will have to do some panorama-style cropping -- an uncropped image will print a 12x18, so you will need to decide whether to crop a bunch or do some "creative framing". But think this through -- if you print at say 100 ppi, that would require a file size of 1200x4800 pixels but would produce a sub-par quality print. Up that to 150 ppi and you need 1800x7200 pixels, which is more of a printable quality.

For a composite, I don't see a big problem with using a 300 ppi image, but you can get away with a smaller resolution/file size, expecially since as you say you don't need a "crystal clear" print. I'd work with your print lab/shop and do test shots with small crops of the image that you can look at from the planned viewing distance to judge the results.

Thanks Tony. Yes, it will be a composite of several smaller images with some text added as well. We shoot a lot of kids sports leagues, so the idea is to have a large print that shows some of the products we offer. I'm thinking I'll talk to our rep at the lab and make sure a smaller file size at 300ppi would work. Thanks for your input!

Well, cool, you can get "decent" results at, say, 150 ppi, and then the quality of the print just keeps going up with the more resolution.

You should understand that a smaller size will be a lower ppi. Ppi is pixels per inch, so 12x48 at 300 ppi can only be 3600 x 14400 pixels. However, for a poster that will not be viewed close up resolution in the area of 180 - 200 ppi will be sufficient.

XTshooter wrote in post #11980705
Once designed, we're going to print it through our lab.

If by "our lab" you mean a professional print lab, they're the ones to ask about this. Different labs have different needs.

XTshooter wrote in post #11980705
as I know a full 12" x 48" file in Photoshop would be a nightmare to work on and save.

If you have a halfway decent computer, 3600 x 14400px isn't too bad.
I've done quite a few images with more pixels on an ancient G5.

If you want to work at a lower resolution for the images, you could let the text be vector based, so it will remain sharp.