The minimum distance is 1 mile (or 1km if you're calculating it in km) If you have done 1 ride of 1 mile but have
not done 2 rides of 2 miles then your Eddington number is 1.
No Strava doesn't calculate it. But there is a website written by an ex Cyclechatter that does.
https://cyclingrelated.uk/eddington/
You could, theoretically, use other units. For example for climbing you could use 10m of ascent. So if you have done 100 rides of 100x10=1,000m of ascent but not 101 rides of 1,100m then your metric 10m climbing Eddington would be 100. This would be a really pointless and confusing thing to do. Only a complete nerd would do such a thing. Yes I have done it. No I can't remember what the figure came out to.