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Resize a photo to 45×45 mm (531×531 pixels)
A 45×45 mm print at 300 DPI is 531×531 pixels. Set 45×45 mm and 300 DPI in the panel and choose crop to fill: a 4:3 phone photo loses 25% and still gives 1,707 pixels per inch. As a JPEG, a head-and-shoulders portrait comes to about 50 KB at the panel's default quality 85 and 37.8 KB at quality 75.
45×45 mm at 300 DPI (531×531 px)
JPG · no file-size limit · 45x45 mm at 300 DPI · white background
No file-size limit is set: PixelFit saves at high quality and changes only the format and any pixel size you set. 45x45 mm at 300 DPI is 531x531 pixels.
Fit, background and padding crop to fill · white background
Saving presets is part of Pro.
The result appears here: the exact byte count, pixel size and quality, the size before and after, a preview and a download button.
The batch kit (one ZIP for up to 500 photos, several photos merged into one PDF) is part of Pro.
45×45 mm at a glance
| Physical size | 45×45 mm = 1.77×1.77 in |
|---|---|
| Pixels at 300 DPI | 531×531 px (281,961 pixels, 0.28 MP) |
| Shape | 1:1, square (width ÷ height = 1) |
| From a 12 MP phone photo | 1,707 pixels per inch after the crop to fill (25% cut) |
| Copies per sheet | 6 on 4×6 in · 24 on A4 · 24 on US Letter |
| At 600 DPI | 1063×1063 px (1.13 MP) |
| Resampling passes from a phone photo | 3024×3024 crop → 1512×1512 → 756×756 → 531×531 |
| Estimated JPEG (portrait photo, quality 75, 300 DPI) | 37.8 KB |
| JPEG without a KB limit (panel default, quality 85) | 50 KB |
How 45×45 mm turns into pixels
An inch is exactly 25.4 mm, so at 300 DPI the pixel size is 45 mm ÷ 25.4 × 300 = 531.496, rounded to 531 px wide, and 45 mm ÷ 25.4 × 300 = 531.496, rounded to 531 px tall. 45×45 mm is square, 1.77×1.77 in in the other unit.
The same 45×45 mm needs 354×354 px at 200 DPI and 1063×1063 px (1.13 MP) at 600 DPI. PixelFit writes the DPI you set into the JPEG header (the JFIF density field), so print software that reads it knows the file is meant to come out at 45×45 mm.
Is your photo sharp enough for 45×45 mm?
After the crop to fill, this is how many source pixels land on each inch of 45×45 mm. Above 300 DPI the picture is reduced to 300 DPI; below it, PixelFit has to enlarge the crop and fine detail softens.
| Starting image | Crop to fill keeps | Area lost | Pixels per inch at 45×45 mm | To reach 300 DPI |
|---|---|---|---|---|
| 12 MP phone photo (4032×3024, 4:3) | 3024×3024 (left and right cut) | 25% | 1,707 DPI | reduced (0.18×) |
| 24 MP camera photo (6000×4000, 3:2) | 4000×4000 (left and right cut) | 33.3% | 2,258 DPI | reduced (0.13×) |
| Full HD screenshot (1920×1080, 16:9) | 1080×1080 (left and right cut) | 43.8% | 610 DPI | reduced (0.49×) |
| Vertical phone video frame (1080×1920, 9:16) | 1080×1080 (top and bottom cut) | 43.8% | 610 DPI | reduced (0.49×) |
45×45 mm in pixels at each print resolution
Pixels = millimetres ÷ 25.4 × DPI. The panel uses 300 DPI unless you change it; the file sizes are for a portrait saved as JPEG.
| Resolution | Pixels | Megapixels | JPEG q75 | JPEG q90 |
|---|---|---|---|---|
| 150 DPI | 266×266 | 0.0708 MP | ≈ 13.7 KB | ≈ 21.9 KB |
| 200 DPI | 354×354 | 0.13 MP | ≈ 20.7 KB | ≈ 33.3 KB |
| 300 DPI | 531×531 | 0.28 MP | ≈ 37.8 KB | ≈ 62 KB |
| 400 DPI | 709×709 | 0.5 MP | ≈ 58.6 KB | ≈ 98.3 KB |
| 600 DPI | 1063×1063 | 1.13 MP | ≈ 109 KB | ≈ 194 KB |
Will a 45×45 mm photo fit a KB limit?
Saved at 300 DPI (531×531 px), a head-and-shoulders portrait of 45×45 mm comes to about 29.3 KB at JPEG quality 60, 37.8 KB at 75 and 62 KB at 90, and about 22.7 KB as WebP at 75. Dropping to 200 DPI (354×354 px) brings quality 75 down to about 20.7 KB, but the print then holds fewer pixels per inch.
At 300 DPI the photo fits under 20 KB up to quality 31 and under 50 KB up to quality 84; under 100 KB and 200 KB it fits even at quality 95. Set the KB limit next to the size and PixelFit picks the highest quality that fits.
Printing 45×45 mm copies
Without margins or cutting gaps, 6 copies fit on one 4×6 in (102×152 mm) photo print, 24 on an A4 sheet, 24 on US Letter (some turned sideways where that packs more). Print at 100% scale, never "fit to page", or a small ID photo of 45×45 mm comes out the wrong size; 531×531 px at 300 DPI is exact.
Other 1:1 print and photo sizes
These sizes have the same 1:1 shape as 45×45 mm, so a photo cropped for one fits the others with no further crop.
| Size | Pixels | Scale from 45×45 mm |
|---|---|---|
| 2×2 inch photo | 600×600 | 1.13× |
| 51×51 mm photo | 602×602 | 1.13× |
| 35×35 mm photo | 413×413 | 0.78× |
| 8×8 inch print | 2400×2400 | 4.52× |
| 12×12 inch print | 3600×3600 | 6.78× |
| 512×512 PWA icon | 512×512 | 0.96× |
| 500×500 square | 500×500 | 0.94× |
| 600×600 square | 600×600 | 1.13× |
How to resize a picture to 45×45 mm
-
Add the picture
Drop, paste or pick the photo in the PixelFit panel at the top of this page; it is decoded in your browser and never uploaded.
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Set the size
Pick mm as the unit, enter 45×45 mm and 300 DPI; the tool turns that into 531×531 pixels.
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Choose how it fits
Choose crop to fill to keep the 1:1 frame without stretching (a phone photo loses 25%, left and right cut). Fit inside keeps the whole picture as a 531×398 file instead; Pad with colour puts that on a full 531×531 canvas.
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Pick the format and download
Keep JPG (without a KB limit PixelFit saves at quality 85, about 50 KB for a head-and-shoulders portrait) so the 300 DPI stamp travels with the file, or choose PDF to get the picture as a PDF page, then download.
Sources
- Inch (1 inch is exactly 25.4 mm), Wikipedia, checked 31 October 2026: en.wikipedia.org/wiki/Inch
- Measured by PixelFit with sharp 0.35.5 / libvips 8.18.7 on 31 October 2026, from the sample photo President Barack Obama.jpg by Pete Souza (Official White House photo) (Public domain): commons.wikimedia.org/wiki/File:President_Barack_Obama.jpg
Frequently asked questions
How do I resize a photo to 45×45 mm?
Open the photo in the PixelFit panel on this page, set 45×45 mm at 300 DPI (531 × 531 px), choose crop to fill and download. From a 12 MP phone photo that crops 25% (left and right cut) and still leaves 1,707 pixels per inch to work with.
How many pixels is 45×45 mm?
45×45 mm is 531×531 px at 300 DPI, 1063×1063 px at 600 DPI and 266×266 px at 150 DPI (pixels = mm ÷ 25.4 × DPI).
What DPI should a 45×45 mm photo have?
PixelFit uses 300 DPI, which makes 45×45 mm exactly 531×531 px; print it at 100% scale. At 150 DPI the same 531×531 pixels would print 3.54×3.54 in, twice as large and with half the density.
How many 45×45 mm photos fit on one sheet?
Without margins, 24 fit on A4 (210×297 mm), 24 on US Letter and 6 on a 4×6 in photo print, turning them sideways where that packs more. Leave a few millimetres for cutting.
How big is a 45×45 mm JPEG at 300 DPI?
For a head-and-shoulders portrait about 37.8 KB at quality 75 (29.3 KB at 60, 62 KB at 90, 50 KB at the panel's default quality 85); a detailed outdoor photo is about 71.4 KB at quality 75, estimated from measured encodes of real sample photos at 531×531 px.
Related
Same 1:1 ratio
Nearby sizes
- 40×50 mm photo 472:591 (about 4:5)
- 640×480 (VGA) 4:3