To treat pain, the typical recommended dosage of aspirin for an adult is 325 to 650 milligrams every four hours, according to Drugs.com. No more than 4 grams of aspirin should be taken in 24 hours. The same dosage is used to lower fevers.
Some adults take aspirin every day under doctor's supervision. The usual dose to help prevent heart attacks ranges from 81 to 325 milligrams, states Mayo Clinic. Adult patients with arthritis often take 3 grams of aspirin divided into multiple doses, Drugs.com says. A daily dose of 75 to 325 milligrams is sometimes used to prevent a stroke. If an adult has already had a stroke, 50 to 325 milligrams of aspirin is prescribed.