Health bars indicate to the player how much health they have before death.
Health bars have the option to include a unit on which to measure their current health in relation to the maximum health available.
When to use
Games that include combat mechanics may want to feed back to the user the current status of the health.
When vehicles can receive damage, the health bar may represent how durable the vehicle is and how long until a vehicle becomes unusable.
The colour red is often used to represent health, this is usually because it represents the colour of blood. The colour red has been used to represent health and aid before video games with the red cross being the symbol of the combat medic.
Icons are optional, although most games that include health bars will use icons (typically a heart) to aid recognition.
It is highly recommended that health bars are given units of measurement. This allows players to accurately assess gameplay situations at a glance.
Tap on or hover over an example thumbnail to view the context of the Health Bar, if a screenshot exists.
Heroes of the Storm
Smackdown vs Raw
Mortal Kombat 2
League of Legends
Horizon Zero Dawn
For any games that include death or combat, it is recommended that the health bar is displayed at all times of gameplay, or at the very least during situations which would result in death or loss of health.
Concerning iconography and health bars, some games such as Minecraft will use icons as a health bar. The heart icon is a famous symbol to represent health.
This needs more details. A great example of a highly detailed health bar is Heroes of the Storm: White portion represents temporary health (shield), orange portion represents damage over time. Dark green represents heal over time. Ticks represent absolute numbers (as opposed to the bar % which is relative). Many games also use flashing red portions to illustrate damage happening.