Understanding DPI and Resolution for Poster Printing

It isn’t always easy figuring out what kind of file you need to print an image and once you get into large format, it becomes even more difficult. Hopefully, this article will help you figure out what is needed when printing large format posters and displays. We should start with some clarifications of the terms we will use.

Large Format is the term we use for prints that are larger than what typical digital presses can handle or something that will be printed on our large format printer. In our case, large format would apply to any of the poster items.

Resolution is the measurement of the pixel count a camera can output or that a image file was created at. Pixels are the number of dots horizontally across an image multiplied by the number of pixels vertically of the image. When you see that an image is 2000 x 3000, that number is the resolution. This number is often used when measuring a camera’s picture quality. High resolutions usually only help when blowing up a picture for large format. You can tell what an image’s resolution is (on a PC) by right clicking it and selecting properties, then clicking details. On a MAC you can find this by right clicking and going to “Get Info”.

DPI stands for Dots per Inch. This is the measurement of clarity or quality of an image. The number of pixels in a square inch of the image is how DPI is determined.

Alright, with those terms out of the way, let’s get back to how to figure out what resolution and DPI you need to print. It is a sliding scale depending on a few factors: distance of the viewer from image, size and intended use of the print. Resolution determines the size you should print and DPI determines distance it should be view from.

 

If you are viewing an image from close up you should have somewhere between 250-300 DPI. If you are a few steps back you can probably get away with between 150 and 250 DPI. The farther back you go, the lower the DPI can be. The eye tends to clump details together as distance increases. If this is an outdoor display and the viewer is going to be even farther away, you could go as low as 70 DPI. If you ever get the chance, go look at a billboard up close. Chances are it is really bad quality, but looks great when driving by.

There is a simple formula you can use to figure out how large you can go or how large you should go based on intended use. The goal here is to not resort to re-sampling the photo using software. Ready for some math?

 

Resolution/dpi = print size (use known resolution divided by desired DPI for each dimension).

Ie. 2000 x 1500 image at 200 dpi means I can print an image at: 10”x7.5”

2000/200 = 10  and  1500/200 = 7.5   which means  10×7.5.

 

Dpi x print size = resolution (use desired DPI times desired print size for each dimension).

Ie. I want to print a 16×20 at 250 DPI. My image would have to be: 4000×5000.

250 * 16 = 4000  and  250 * 20 = 5000  so…. Resolution = 4000×5000

 

So now that the math part is done, you know roughly how to figure out what you need to print what you want when it comes to large format. There is usually no point going higher than 300 DPI as the human eye has trouble picking up anything higher than that anyway. Here is a chart you can use as a sort of large format cheat sheet.

Size

100 DPI  Resolution

200 DPI Resolution

300 DPI Resolution

12 x 16

1200 x 1600

2400 x 3200

3600 x 4800

16 x 20

1600 x 2000

3200 x 4000

4800 x 6000

20 x 24

2000 x 2400

4000 x 4800

6000 x 7200

20 x 30*

2000 x 3000

4000 x 6000

6000 x 9000

24 x 36*

2400 x 3600

4800 x 7200

7200 x 10800

30 x 40*

3000 x 4000

6000 x 8000

9000 x 12000

36 x 48*

3600 x 4800

7200 x 9600

10800 x 14400

*We currently don’t offer all of these sizes online, but this just gives an idea of how it scales.

7 thoughts on “Understanding DPI and Resolution for Poster Printing

  1. Posters Printing are very important develop one’s business.
    Thanks for providing such information.
    Thanks for sharing the post.
    Keep sharing more and more.

    • In the name of trinity one God amen. hello broehtrs and sisters in christ we really appreciate the comment you all are giving. it is really very help full for our solidarity. the group is yet organizing itself, you could imagine that there could be some flaws. so we believe any comment from you (true tewahedo followers) could be constructive for our progressive strength and solidarity. please don’t hesitate to give any comment, suggestion and feedback. together we can avoid mistakes and exert big impact .God bless you all ስለ ምትሰጡን ማንኛውም አስተያየት ከልብ እናመሰግናለን። በአንድነት ለመጠንከራችን በጣም ጠቃሚዎች ናቸውና።ይህ ህብረት ገና እየተደራጀና እየተስፋፋ ስለሆነ ድክመቶችና ስህተቶች ይኖራሉ በለን እናምናለን። ስለሆነም የእናንተ አስተያየት ለቀጣይ ጥንካሬና ብርታት ገንቢ ጎን አላቸው ብለን እናምናለን። እባካችሁን ማንኛውንም አስተያየትና የማሻሻያ ሃሳቦችን ለመስጠት አታመንቱ እንላለን። ተባብረን ችግሮችን ማስወገድና ትልቅ ጫና ልናደርግ እንችላለን። እግዚአብሄር ቤተክርስቲያንን ይጠብቅልን ሀገራችንን ይባርክልን

  2. Good info, but it seems like there is a serious inconsistency with what you are teaching here. You taught that when calculating DPI from resolution you:

    “Resolution/print size = dpi (divide each dimension by desired print size and then add the two values together).”

    If you are supposed to add the two values together then why when teaching how to go backwards (calculationg Resolution from DPI) did you not start by dividing the DPI consistent with the ratio 16X20?

    “Ie. I want to print a 16×20 at 250 DPI. My image would have to be: 4000×5000.

    250 * 16 = 4000 and 250 * 20 = 5000 so…. Resolution = 4000×5000″

    Does my question make sense, because it seems to me, What you taught does not make mathmatical sense.

    • You are right! Thanks for pointing this out. I took it back to our graphic people to have another look and they see the mistake made originally. I am told don’t bother adding. Your dpi will be the lowest number technically, since the goal here to to determine what size you can print without “re-sampling” to fake your way to a better dpi. I’ll fix that up in the article.

      Thanks again!

  3. Interesting article – thanks for the detail. One thing that I’m also interested in knowing, is what kind of camera you need in order to be able to take photos of 10800 x 14400. You say you don’t want to resort to re-sampling, but how do you get such high resolution? I have a Canon 5D Mark III and the photos are just 5760 x 3840 – which wouldn’t even get me a 16×20 inch print.

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