I'm not aware of any formal ratio for levies before the Code of Service of 1556, which obliged a landowner to produce a man, "on horse and in armour complete" for every 100 chetvert's of land they own, something like 5000 square meters. Actually the definition of a chetvert' as a unit of area was variable so it's not very helpful, but the ratio would be much lower than 1:10. But with the adoption of this code, more landowners were being called on to raise soldiers than before, which relaxed the burden on the state treasury.
Five thousand square meters is a little over an acre. I'm seeing a huge range of estimates for what a chetvert was, but 500,000 m2 = 120 acres should support six households, or 30 people, on reasonably fertile ground. Six households of poor tenants, that is -- 40 acres would be an ideal size for a freeholder. So, three to six households maybe? - but less if the land is marginal.
Note also that in the Anglo-Saxon system, acres represented a fixed unit of crop yield but variable land. So, three area acres of land could go down in the documents as one fiscal acre.
In the Anglo-Saxon fyrd, I believe, normally households would pool their resources to contribute one reasonably well-equipped and trained warrior to the host at the ratio of five households to one warrior. Cavalry cost more. In the 11th century Byzantine system, different troop types were given differently-sized estates to support them. A cataphract had an estate that would normally support 30 families. A lighter cavalryman had an estate that supported 15 families.
To sum up, I'd say that most levy systems were designed to encourage a group of farmers to find their biggest, most aggressive member, have him practice a lot between campaigns, and send him off with decent equipment and maybe even a horse, rather than send a half dozen guys with no aptitude for fighting.
There are good operational reasons for this. Medieval armies tended to cap out at 10,000 to 30,000 men, often much less, because anything larger could not sustain itself by foraging along the line of march. Bigger armies take longer to form up for battle and longer to leave camp.
If an army in a battle has a lot of untrained peasants, they're probably from nearby and fighting in defense of their homes, or are camp followers.