Thumbnail dimensions

[Kate Bowling]

a lot of our internal customers like to design custom thumbnails for their videos and i've been asked what the correct dimensions are. google is failing me. does anyone know the best dimensions to use when creating a thumbnail? thanks!

[#2]

It needs to be 16x9 aspect ratio, otherwise you'll get black bars on top or sides. ~1000 px wide is fine. Uploading a ~4000px+ wide image is overkill.