Objective. Intentional or unintentional substance intoxications are common in patients presenting to the Emergency Department (ED). When we treat intoxicated patients, it is important to know the amount of drug ingestion. We invested the actual amount of semi-quantitative term expressed by patients, and investigated the accuracy of amount estimates by the public and healthcare professionals. Participants and interventions. 200 volunteers (86 health care providers and 114 non-practitioners) participated. Participants grabbed the 3 types of tablets (5mm, 10mm, and 15mm) in handfuls and fistfuls and estimated the tablet amounts. Actual amounts were measured. 100 volunteers (58 health care providers and 41 non-prac-titioners) participated in the investigation of accuracy of liquid amount estimation. Participant ingested water in 2.6 cm diameter bottle in response to request to take 1 sip, 1 mouthful, and 3 sips. Results. The estimated tablet counts became more accurate in terms of both fistfuls and handfuls as the size increased within the same shape classification. Participants tended to underestimate the counts of oval-shaped tablets to a greater extent than round tablets of the same size. The estimated liquids both groups of participants tended to underestimate the amounts but both groups overestimated the volumes when drinking 3 continuous sips. In tablets and liquids, there were no statistically significant differences in accuracy between the groups. Conclusions. When approaching intoxicated patients who have visited emergency department (ED), treatment should be implemented based on the assumption that the actual ingested amounts are higher than the amounts estimated by patients.