A consistent icon set is one whose icons are designed following the same strict rules. Before you start drawing icons for a set, create a list of rules that all icons in the set must follow. You need to decide the rules for the line width, colors, corner shapes, spacing etc. and closely follow these for all icons. For example, if you set a rule for the line width to be 1.5 and the colour to be #E51919, then all the icons in the set must have the line width of 1.5 and have the color #E51919.
For an in-depth tutorial on creating consistent icon sets, check out our blogpost Better Icon Design in 6 Easy Steps.
Keeping a consistent style across icons in an icon set is critical for the value of the set as a whole. When the style is inconsistent, it becomes difficult for the users to use the icons together and create a great looking design. Keep a close eye on line widths, gradients, gloss, textures, labels etc. The critical areas to get right are:
Stroke width is important to keep consistent to achieve a professional look of your icons. You should be careful about using too thin lines since many users will use your icons in small sizes e.g. in a mobile app. Thin lines will disappear when scaled down. Pick line-widths that are visible even when the icon is scaled down.
If you use effects such as shadows, gradients and gloss, make sure that these are used consistently.
If you're using background shapes for your icons, make sure that all of them are having the same shape. Having different ones like squares, circles, triangles etc. will not look consistent an might be rejected during our review process.
Visual size of the icons should be consistent. It’s not enough to make sure the icons all have the same height and width in pixel. Some icons might have a larger area e.g. a house icon, compared to a plus sign, even if their weight and hight in pixels are the same. These two icons would appear in different sizes even though they have the same height and width in pixel. To adjust the sizes of your icons, you should view them all together in an overview and try to spot the icons that stand out and scale them until no icons stand out. If icons look different sizes, this could also be caused by their artboard sizes. Read more about Artboards.
The design style within a given set should be consistent among all icons in the set. For instance, if your set is outline style, then all icons in the set should be outline style. Do not mix glyph, flat, or 3D icons in an outline set. By the same token, if your set is a glyph icon set, do not mix flat, outline, skeuomorphic, cartoon, etc. styles with a glyph set. Our review team will reject sets with inconsistent design styles, background, shapes, or background colors, with a request to make the consistent.