> For the complete documentation index, see [llms.txt](https://docs.unisphere.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.unisphere.io/unisphere-apis/explanatory-notes/speeds.md).

# Speeds

The difference between Equivalent Airspeed (EAS) and Ground Speed (GS) lies in what they measure and the factors they account for:

**Equivalent Airspeed (EAS):**

**Definition**: EAS is the airspeed corrected for changes in air density due to altitude and atmospheric conditions. It represents the dynamic pressure acting on the aircraft.

What it measures: It shows the aerodynamic performance of the aircraft and is primarily used for understanding flight dynamics, such as stall speed, maneuvering limits, and structural loads.

Key Factors: EAS is influenced by air density (altitude and temperature) but does not account for wind.

**Ground Speed (GS):**

**Definition:** GS is the actual speed of the aircraft relative to the ground. It's the speed at which the aircraft is moving over the Earth's surface.

What it measures: It shows how quickly the aircraft is traveling from point A to point B on the ground.

Key Factors: GS is influenced by true airspeed (TAS) and wind. A tailwind increases GS, while a headwind decreases it.

**Key Differences:**

Purpose: EAS is related to aerodynamic performance; GS is related to navigation and how fast you reach your destination. Altitude & Wind: EAS accounts for air density but doesn't include wind effects. GS includes wind (headwind/tailwind) but doesn't consider air density.

For example, an aircraft can have a high EAS but a low GS if flying into a strong headwind.