# Understanding Driving Efficiency

Tessie measures the energy efficiency of your driving in a few different ways:

• Range Efficiency – Range efficiency measures the amount of range consumed versus the amount of real-world range driven. For example, if you used 100 miles of range, but only drove 99 miles in the real world, that drive would be 99% efficient.
• Total Energy Used – The total amount of energy consumed over the course of a drive, factoring in all real-world conditions.
• Average Energy Per Mile/Kilometer – The total energy used divided by the distance driven.

If energy efficiency numbers differ between Tessie and your Tesla

Measuring true battery energy and energy expenditure isn't possible without using special lab equipment, so your Tesla (and Tessie) provide estimates. Because they are estimates, the numbers will differ. The in-vehicle energy display uses a unique calculation will skew the number lower than the true amount. Tessie uses a straightforward calculation, shown below.

Prior to finishing a charge of at least 5 kWh, Tessie uses the default EPA rating for the vehicle for energy efficiency estimates which may be off. After charging, Tessie learns your battery pack and will provide more accurate estimates.

How Tessie calculates energy usage and energy efficiency

Here's an example:

If your battery is charged to 100% and has a 100 kWh capacity, and your battery goes from 100% to 75% after a drive, that means the drive used 25 kWh.

If the drive was 75 miles: 25 (total kWh used) / 75 (total miles driven) = 0.333 kWh/mi = 333 Wh/mi.