Run the nvidia-smi command.

Get the name/model of your NVidia card, then find it on this page: https://developer.nvidia.com/cuda-gpus

So below, you can see my GeForce GTX 950 has a computer power of 5.0:

The reason for checking this was from a blog on Medium regarding TensorFlow. It said:
Check for compatibility of your graphics card. The latest environment, called “CUDA Toolkit 9”, requires a compute capability of 3 or higher.