How many small fish can i fit in a 10 gallon aquarium?

It is NOT by size of fish. Someone has told you stocking is based on inch per gallon. This is wrong. Stocking is based on what the species' needs, and you aren't doing well so far I'm afraid! Swordtails are far too chunky for a 10g, they really need no smaller than 25-30g. Big bolshy fish. Similar goes for Platys - very active fish and need at least 20-25g. The X-Ray Tetra cannot be kept alone, it HAS to be in a group of 6 or more, it's too large a Tetra to be kept in a small 10g. I would recommend either upgrading to a much larger tank or rehoming the fish you have and starting again! http://www.theaquariumwiki.com/10_Gallon

1inch/gallon excluding goldfish. Based on what you're interested in, I don't recommend a betta for a smaller tank like that. Anything remotely colorful and pretty =competition to a male betta and he will chase them. A female betta will be less aggressive. However, given the types of fish you bought, they are all "community" fish and like to be in groups with similar types. Right now you have 7 gallons of fish, so you have room for only another 3 inches. Try getting a couple more x-ray tetras for now so they can school.

The 1'/gal rule is a go by for keeping a fish alive. However, the type of fish determines what makes it happiest. Some like big runs, some grow big, some like shade, some like a certain water quality, some can't get along, some need groups etc.... For now, the 1"/gal rule is fine and making sure they all get along. Here is where your headed next..........."I need a bigger aquarium, they are getting bigger and I want my baby to be happy"....then you buy a 20 gal.....then 30....then...well you get the picture. If you have the cash, just invest in a 30 gal next if you like having an aquarium. Not many fish need anything bigger than this.

10 gallons is too small for tetras. They need room to swim. 10gallons is large enough for a couple of platies and a betta. that's all.

add 2-3 pairs of guppys and your tank is fully stocked

The 1'/gal rule is a go by for keeping a fish alive. However, the type of fish determines what makes it happiest. Some like big runs, some grow big, some like shade, some like a certain water quality, some can't get along, some need groups etc.... For now, the 1"/gal rule is fine and making sure they all get along. Here is where your headed next..........."I need a bigger aquarium, they are getting bigger and I want my baby to be happy"....then you buy a 20 gal.....then 30....then...well you get the picture. If you have the cash, just invest in a 30 gal next if you like having an aquarium. Not many fish need anything bigger than this.

1inch/gallon excluding goldfish. Based on what you're interested in, I don't recommend a betta for a smaller tank like that. Anything remotely colorful and pretty =competition to a male betta and he will chase them. A female betta will be less aggressive. However, given the types of fish you bought, they are all "community" fish and like to be in groups with similar types. Right now you have 7 gallons of fish, so you have room for only another 3 inches. Try getting a couple more x-ray tetras for now so they can school.

10 gallons is too small for tetras. They need room to swim. 10gallons is large enough for a couple of platies and a betta. that's all.

add 2-3 pairs of guppys and your tank is fully stocked