How big is big enough for a photo’s DPI

How many megapixels do you need? The short answer is, not a lot if you are just e-mailing photos to friends and family.

'Woman Reborn' was enlarged to 20 inches square at 220 dpi and was part of an exhibition at Presentation House in North Vancouver.

I am sitting in my studio/workshop listening to the Beatles and looking out at the glorious sun that is streaming in the south-facing window. What a perfect Port Alberni day.

What a perfect day to be out with a camera practicing the eight steps to perfection.

Cameras, they are all around us these days hidden in cellphones, iPads, iPods, eyeglasses, pens, hats and so on. I am sure that they all have their uses, but don’t expect to be making wall size murals.

Here are some facts about those hidden cameras:

iPad 2

Rear camera: 0.9 megapixels

Front camera: 0.3 megapixels


Camera: 5 megapixels

iPod Touch

Rear camera: 0.7 megapixels

Front camera: 5 megapixels


Curve 8520

Camera: 5 megapixels

Nintendo DSI

Camera: 0.3 megapixels

T-mobile my touch

Camera: 3.2 megapixels

HTC Droid Phone

Camera: 8 megapixels

How many megapixels do you need? The short answer is, not a lot if you are just e-mailing photos to friends and family.

If you are going to be blowing photos up to 11” x 14” or larger then you need lots of megapixels. Here is a chart for the perfect printing resolution:

Print size 300 DPI:

4”x 6”— 2.2 megapixels

5”x 7”— 4.0 megapixels

8”x 10”— 7.3 megapixels

11”x 14”— 13.9 megapixels

13”x 17”— 20 megapixels

20”x 30”— 54 megapixels

Why 300 DPI? That’s the resolution at which the human eye would have trouble seeing the dots in the photo (300 DPI translates to a one inch square that has 300 dots x 300 dots = 90,000 dots or 0.09 megapixels).

When you blow up your photos to 20”x 30” or larger then you can get away with a lower resolution because the image is viewed from farther away.

A 10 megapixel image would  produce an acceptable 20” x 30” print at 200 DPI. A 10 megapixel image would measure 2500 pixels per inch x 4000 pixels per inch.

As you magnify the image, you magnify the faults as well.

Play around with Photoshop or take one of my courses  at North Island College. I am teaching “How to use your digital camera” as well as “BYOB” Mac 101class, and “Photoshop Elements for beginners”.

I am now going to repeat myself and say “back up your hard drive”. Attach an external hard drive of at least one terrabyte.

If you are lucky enough to own a Mac then it is child’s play. The program called “Time Machine “ will walk you through the process. The program will automatically record a backup of the latest data every hour.

Important data such as contracts, photographs, and addresses  should also be burned to DVDs. Hard drives are far from perfect so double save.

Any questions?  E-mail me at

Norman Silverstone teaches photography through North Island College and Eldercollege in Port


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