It’s pretty easy to make custom wallpaper (background images) for your smartphone. The main trick is getting the size right. Of course, as with so many things associated with modern smartphones (and consumer goods in general) close is usually good enough. And with most things regarding digital images, too big is better than too small.
STEP 1: Determine the Aspect Ratio of Your Phone
“Aspect Ratio” is the term for height-to-width ratio of a display screen (or an image). You want the aspect ratio of your image to match the aspect ratio of your phone. To determine your phone’s aspect ratio you need to know its resolution. That is, its screen size (height and width) in pixels.
• For iPhone screen resolutions try this web site
• For most other phones use this web site site
Or you can just do a web search on “screen resolution” plus the make & model of your own phone.
When you have your phone’s screen dimensions divide the smaller number by the larger number; you should get a result somewhere between 0.4 and 0.63. Find the closest number in the left-hand column of this chart and use the matching ratio in the right-hand column:
| Small dimension/large dimension | Ratio |
|---|---|
| 0.40 | 5:2 |
| 0.46 | 13:6 |
| 0.47 | 19:9 |
| 0.56 | 16:9 |
| 0.63 | 8:5 |
Here are some typical phone displays:
| Phone Make & Model | Width | Height | Approximate Ratio |
|---|---|---|---|
| Samsung Galaxy Tab A10 | 1200 | 1920 | 0.63 (8:5) |
| Samsung Galaxy A10 | 720 | 1520 | 0.47 (19:9) |
| Apple iPhone X | 1125 | 2436 | 0.46 (13:6) |
| Apple iPhone 11 Pro Max | 1242 | 2688 | 0.46 (13:6) |
| Samsung Galaxy S9 | 1440 | 2960 | 0.40 (5:2) |
If you can’t find the screen resolution of your phone or just want to make an image suitable for a variety of phones use the 16:9 (0.56) ratio of high-definition television. This will work with most devices without excessive cropping and/or scaling.
STEP 2: Cropping the Image 
- Choose the image you want to use as wallpaper and open it in Photoshop. Use the original image in full resolution if possible. The bigger the image you start with the better your final result will look.
- Choose the Crop Tool from the toolbar. Pick “Ratio” from the drop-down list at upper left. If you’re making a generic 16:9 wallpaper enter 9 for the width and 16 for the height; if you’re making a wallpaper image for your own phone you can enter the ratio for the specific phone you have — the example shown at right is for a 13:6 ratio.
- Click once within the crop area to activate the tool and guides; now you can adjust the size, position and rotation as you see fit.
- When you’ve achieved your desired look click the check mark on the right side of the Options Bar.
- Save the image as a Photoshop PSD file under another name at this point; this will be your master for making wallpaper images using this design.
STEP 3: Scaling the Image
- Now you should re-size the image for use as phone wallpaper. Phones will automatically scale the image to fit, but there’s no value in making the image too large — it’ll just take up more storage space in the phone’s memory. On the other hand, making the image too small may reduce image quality to an unacceptable level.
- If you’re making wallpaper for general use — to work on a wide variety of phones — pick the largest dimensions it’s ever likely to need. From the phone chart above you can see the Samsung Galaxy s9 has a screen that measures 2960 pixels along the long axis. Its successor, the s10 is 3040 x 1440 and there may be even higher resolution screens on the market by the time your read this. Even so, going with 3000px on the long axis should suffice.
- If you’re making wallpaper specifically with your own phone you should use the dimensions you looked up earlier.
- From the Photoshop menu choose Image > Image Size…
- Choose “Pixels” as your unit of measurement and make sure the Resample box is checked.
- Enter either the height or width of your desired image size in the appropriate box then press the Tab key; if you’ve done everything right, the other dimension should automatically update to the correct height or width; if not, go back and scale or crop your image as necessary (or check your math!)
- When you have the correct dimensions in the Image Size dialog click OK.
- Now save the image as a JPEG file; from the Photoshop menu choose File > Save As and pick JPEG from the file format list, un-check the Embed Color Profile box and then click OK.
- In the JPEG dialog — Put the Quality setting at 8, set the Format Options to Baseline (“Standard”) and then click OK.
- You’re done! Move both the PSD original and the re-sized JPEG somewhere for safe keeping. Copy the JPEG to your phone and choose it as your wallpaper through the system settings (which will vary depending on what OS your phone runs).
Rules of Thumb for Phone Wallpapers
- If in doubt use a 16:9 ratio — most phones will work reasonably well with that.
- Try to keep important elements in the photo away from the edges (so they don’t get cropped out on phones with different aspect ratios).
- Size the final image to about 3000 pixels on the long axis or use the exact size of your phone screen.
