You are a product delivery manager at Amazon. Estimate how many face masks Amazon needs to stock in UK stores during the COVID-19 lockdown period.

First attempt at answering an estimation question. Please provide feedback

Clarification Questions:

1. What Kinds of Masks are we talking about (Disposable, re-usable, N95 etc.)
2. Time frame of the stock-up

Assuming disposable masks.  Assuming time line is 3 months

 Formulae : Number of people using the disposable masks * number of masks used in a month * 3

Population of UK: 65 Million.

Assuming equal split age wise - 0 - 80: 812,500 in each age

Ages 0 - 5 : 

• Parents not taking them out and are at home. 
• Not wearing masks at all - 4 Million Approximately

Ages 6-21 : 

• 50% of them wear masks and half dont. approximately: 6 Million
• Out of the 50% who wear masks, half of them use DIY masks: Approximately: 3 Million
•  step out twice a week. 8 times a month. 
• Assuming half of them re-use their masks at least one time more:
• Number of masks in 3 months: 4 masks a month * 3 million = 12 Million

Ages 22-60: 

• 25% of them dont venture out at all. Remaining masks users: Approximately: 23 Million
• 75% of them wear masks. Approximately: 17 Million
• Some are already sick at home and hence dont venture out. 
• The people venture out once a week for errands. 4 times a month. They re-use their masks  once. 2 masks in one month. 6 Masks in 3 months
• Out of Assumption is that people delivering groceries or frontline workers will get a high grade N95 masks. 
• 25% use DIY masks. Remaining masks users: Approximately: 13 Million
• Number of masks: 13 Million * 6 = 78 Million

Ages 60-80: 

• High chances of getting the covid-19, hence 60% are not going out. Approximately: 6 Million 
• 25% use DIY masks, surgical masks etc. Approximately: 5 Million
• Go out once every other week. twice a month. 1 mask a month, 3 masks in 3 months
• Number of masks: 15 Million

Stock up for 3 months: 12 + 78 + 15 = 105 Million