Can bettas live with cardinal tetras?

Verdict
Yes

Yes. Bettas and cardinal tetras get along in the same tank. Both are fine at 76–82°F. Plan on at least 20 gal.

BettaBetta76–82°F · pH 6.5–7.5 Cardinal tetraCardinal tetra76–84°F · pH 4.6–7

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 76–82°Betta 76–82°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 6.5–7Betta 6.5–7.5Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

Betta · 2.5 inCardinal tetra · 2 in0"1"2"3"4"5"6"
Adult length in an aquarium. A fish can swallow anything that fits in its mouth, roughly a third to half its own length for predators.

Care at a glance

BettaCardinal tetra
Temperature76–82 °F76–84 °F
pH6.5–7.54.6–7
Adult size2.5 in2.0 in
Minimum tank5 gal20 gal
TemperamentSemi-aggressivePeaceful
Swims atTopMiddle
GroupOne per tankGroups of 6+
DietCarnivoreOmnivore

Better tank mates for bettas

All betta tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can bettas live with cardinal tetras?

Yes. Bettas and cardinal tetras get along in the same tank. Both are fine at 76–82°F. Plan on at least 20 gal.

What temperature suits both bettas and cardinal tetras?

76–82 °F. Bettas need 76–82 °F, cardinal tetras need 76–84 °F.

What size tank do bettas and cardinal tetras need together?

At least 20 gal, set by the cardinal tetra. Add space for each extra fish.