What size in pixels are sheets of A4 and A3 depending on the DPI?

Ноябрь 28, 2019 0 Автор Дмитрий

When preparing images for printing for many users the question arises about the size and aspect ratio. And if with standard paper formats and their sizes of people sign (A4 sheet is 297×210 mm), then transfer them to the pixels having difficulty. Today I will tell you what size in pixels are sheets of A3 and A4 with different image quality.

The number of pixels for A4 sheet depends on the DPI setting you use:

• if dpi=75, A4 is 877×620 px
• when dpi=150, A4 is 1754×1240 px
• if dpi=300, has A4 3508×2480 px
Similarly one establishes the correspondence of points to the sheet size is A3:
• if dpi=75, A4 is 877×1240 px
• when dpi=150, A4 has 1754 x 2480 px
• if dpi=300, A4 is 3508×4961 px


How is the number of points corresponding to the format?

Let’s take a closer look at where these numbers come from and how to count.
For starters, it is important to understand one simple thing – translate the linear dimensions of paper in pixels without additional data it is impossible for the following reason:
For linear dimensions (mm, cm) are not taken into account characteristics such as image quality. The picture quality is determined by the number of points per unit area. You can make a pixel size of 1 sq mm, then a sheet of A4 is equal to 297×210 pixels (this example does not comply with the standards in reality, there are generally accepted standards).
Image quality is generally measured in dots per square inch (dots per inch) – DPI. 1 inch equals 25.4 mm.

Standard sizes DPI used in print:
• 75 suitable for documents with text
• 150 is the minimum for printing photos
• 300 – the best quality for printing pictures
Let’s see the examples of how all this is calculated. When quality data is, can bring it all together and calculate how many pixels will fit into our A4 (297×210 mm).
Calculation of A4 size in pixels at 150 dpi
• height – 297150/25,4=1754 px • width – 210mm150/25,4=1240 px
Calculation of A4 size in pixels at 300 dpi
• height – 297300/25,4=3508 px • width – 210mm300/25,4=2480 px
If the source image has less pixels, it still can be printed on the A4 sheet, but you have to understand that the clarity will suffer. To minimize the negative effect when you print in such situations, try to apply multiple changes sizes (2, 4, 8 etc. times).
In order to avoid any distortion (elongated or flattened objects) should keep the aspect ratio (decrease or increase while the height and width by the same factor)