How a fourth rate differed from a fifth rate

What distinguished a fourth rate from a fifth rate when both could carry 38 guns?

A fourth rate normally had two gun decks, while a fifth-rate frigate carried its main battery on one deck and was structurally smaller.

A viewer asks how a 38-gun fourth rate differed from a 38-gun fifth rate. The fifth rate would normally concentrate its battery on one main gun deck, while the fourth rate carried two. The extra deck implied a larger and heavier hull even when the headline gun count matched. Later ships could stretch the categories as hulls became longer and batteries changed. Rating cannot be read from gun totals without considering arrangement and construction.