Use the table (presented below) as a rough guide when someone asks you how large of a screen you need for your public speaking presentation. 

• 3-5 people 21 inches diagonal (53.34 cm) 
• 5-9 people 29 inches diagonal (73.66 cm) 
• 10-15 people 37 inches diagonal (93.98 cm) 
• 16-35 people 60 inches diagonal (152.4 cm) 
• 36-50 people 72 inches diagonal (182.88 cm) 
• 51-140 people 120 inches diagonal (304.8 cm) 
• 141-220 people 150 inches diagonal (381.0 cm) 
• 221-390 people 200 inches diagonal (508.0 cm) 
• 391+ people 300 inches diagonal (762.0 cm) 

Source: www.bhphotovideo.com