There are too many smart phones and sizes, I have to create a lock screen for a client but dont know what size I should be designing, is there a standard size that applies to all? instead of creating separate sizes for different phones. Since wallpaper can be adjusted, wouldn't one large size fit all?
- Proportions my friend, not size.
The dominant proportion for screens at this time is 16:9... or 9:16 I should say in the case of phones because they are most used in a vertical position.
- Ok. Let's use a "standard" size.
And you can make a high-resolution wallpaper and let the lower resolution phones deal with it. In this case a 1080x1920px size will be fine.
Forget about the declared resolution. That declared resolution is meant for developers to deal with element sizes in designing interfaces for mobile. You need to use native resolution.
And as a lot of phones want to display full HD video (1920x1080) use those same dimensions in a vertical format.
Some exceptions can be made, for example, a wallpaper that is meant to slide as parallax when you swap thru screens can need a different size proportion. But that is a special case.
I have a few approaches:
1. Design for the Largest Phone
I prefer the iPhone 8 Plus screen which has the dimensions of 414 x 736 pixels. Keep in mind by designing for the largest screen size, you'll inevitably be conceding some of the edges of the design on devices where down-scaling isn't occurring at an exact ratio. Not a "deal breaker" in my opinion but worth noting to a client.
2. Design for a Median Screen Size
Screen widths (in portrait view) can range anywhere from 320px to 414px, and screen heights range from 568px to 812px. Averaging these out gets you roughly 367 x 690px. These aren't exact dimensions for any phone on the market, but they are close enough to the standard Android size (360 x 640px), the Galaxy S8 (360 x 740px), and the Pixel 2XL (360 x 720px) to justify designing to those screen sizes. I give the edge to the Galaxy S8 in this instance since Samsung currently has the edge in smartphone market share at the moment.
3. Design for Device Popularity
As mentioned in the previous section, Samsung is the preferential smartphone in the consumer market currently holding about 23% of the market share. What makes this a less reliable option for basis of design is iPhone holding just over 15% and the historical power struggle of Samsung vs. iPhone. In such a volatile market, it wouldn't be wise to base design solely on this data point alone.
4. Take Everything into Account
While you can easily rely on one of these methods, taking all available information into account before crafting a design is the best practice. Before you sketch anything, or open the computer, figure out as much as you can. Solving the problem (in this case, which screen size will best exhibit the design vs. which screen size will best represent a universal experience) first requires the designer to gather information. The more information, the easier the puzzle becomes and the easier it will be to talk to your client about your solution.
Another answer is to design this in a vector app (Illustrator, Affinity Designer, Inkscape) so that it's resolution independent, and then set up correct batch export parameters for all the most common resolutions for .pngs, and also export out a clean svg.
Test to be sure your svg functions as expected, and if not, you can distribute the pngs.