Not as a rule. In everyday use the words prawn and shrimp are often used interchangeably, and there is no universally accepted difference between them among the general public, so a large animal sold as a prawn in one country may be sold as shrimp in another. Many commercially important prawns are large: the Queensland Museum notes that the giant tiger prawn (Penaeus monodon), the world’s largest prawn, can reach 35 centimetres in females.
Biologists separate the two by anatomy rather than size. Dendrobranchiate prawns have claws on their first three pairs of legs, while caridean shrimps have claws on only the first two pairs. The easiest check is the abdomen: on a shrimp, the second abdominal segment overlaps both the first and third segments, while on a prawn there is practically no overlap.
Source: Queensland Museum, Prawns and Shrimps
Image: Black tiger and white banana prawns, Pelagic, CC BY-SA 4.0, via Wikimedia Commons.