Can guppies live with cardinal tetras?

Verdict
Yes

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

GuppyGuppy72–82°F · pH 6.8–7.8 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°Guppy 72–82°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 6.8–7Guppy 6.8–7.8Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

Guppy · 2 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

GuppyCardinal tetra
Temperature72–82 °F76–84 °F
pH6.8–7.84.6–7
Adult size2.0 in2.0 in
Minimum tank10 gal20 gal
TemperamentPeacefulPeaceful
Swims atTopMiddle
GroupGroups of 3+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for guppies

All guppy tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can guppies live with cardinal tetras?

Yes. Guppies 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 guppies and cardinal tetras?

76–82 °F. Guppies need 72–82 °F, cardinal tetras need 76–84 °F.

What size tank do guppies and cardinal tetras need together?

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