How long is that cirrus cloud?

I read here https://en.wikipedia.org/wiki/Cirrus_cloud that in certain circumstances a cirrus cloud can be a long as a continent. But what about these? My finger represents 1 degree. I'd say that these clouds subtend 10 degrees. We are in a temperate region so let's say that the clouds are at 6000m. By trigonometry, that puts the clouds at 1km long.