WalkerValleyVet.com recommends half a baby aspirin for dogs under ten pounds and one baby aspirin for dogs 10 to 30 pounds. Half a regular aspirin can be given to 30 to 50 pound dogs; one aspirin for dogs 50 to 100 pounds and two aspirins for dogs over 100 pounds.
WebMD suggests that aspirin should only be used on a short-term basis. Buffered or enteric-coated aspirin is better for a dog's stomach than regular aspirin. While all NSAIDS irritate the stomach, due to the way aspirin metabolizes, one should never exceed the dosages prescribed. A dosage of two regular aspirins could damage the organs of a small to medium-sized dog.