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**Assumes:**
-No ability for clarifying questions.
-A numerical answer is needed.
-Goal is to get right order of magnitude
-Rollers and spherical objects are not considered a wheel.
-Rotational objects where the circumfrance does not make contact on rotation are not wheels (i.e. fans)
-Objects that are wheel shaped but do not rotate are not wheels.
-No Fermi approach.

**Method:**
-Capture the fat head of categories that make up an estimated 80% of wheels.
-Capture the fat head of producers or items in that category that make up 80% of the production output.
-Add in a rough estimate for long tail at end.

shopping cart wheel - https://en.wikipedia.org/wiki/List_of_supermarket_chains - 

120,491 international grocery chains
108,995 * 300 carts for average grocery store = 130,794,000 wheels.
11,496 * 600 carts for average Walmart = 27,590,400 (Walmarts are larger and require more carts)


car wheel - Total Registrations 1,431,448 - https://en.wikipedia.org/wiki/Motor_vehicle#Ownership_trends * 5 wheels (4 + steeringwheel)  7,157,240 wheels.


bicycle wheel - Assume every 1/4 people globally own a bike, 8B people = 2B bikes. = 4.2B wheels (.2b from training wheels sold as a proportion.

wheelbarrows - avg farm is 2 hectares max, and feeds 16-ish people equivelent from food, puts global farms at roughly 500M. Best report to back that was 2014 estimate of 570M farms so roughly in line - https://www.fao.org/family-farming/detail/en/c/281544/  = 570M wheels.

tractors - 125M farms would have tractors, 2 wheels + steering wheel = 375<

Lawnmower - 81% of American households have a yard (https://www.businesswire.com/news/home/20190401005679/en/New-Research-Confirms-Americans-Still-Value-Lawns-and-Green-Spaces), 139M homes, likely similar in Canada 13.82M homes, Aus 8.3M homes, can assume each of these likely has a lawnmower whether they use it or not = 644,480,000 wheels.

toy cars - Hotwheels boasts 4B cars sold (https://hobbylark.com/collecting/1968-hot-wheels-car-list), Matchbox only 3B. 4 wheels each, steering wheels here don't count as they don't actually rotate. These two make 98% of the market = 28B wheels

bags - sammsonite does 3.6B/year in sales (https://www.statista.com/statistics/252796/total-revenue-of-samsonite-worldwide/). Introduced wheels in 1974 (https://www.samsonite.co.id/en/history-of-samsonite/) but didn't catch until 2004 with their four rotating wheels. Avg product price is $450, means they sold 8M items last year. 80% are luggage, 80% of which have wheels. 5,120,000 * 18 years for wheeled luggage 92160000 * 4 wheels = 368,640,000.


Hospitals - estimated post COVID that there are 3 hospital beds per 1000 people globally: https://data.worldbank.org/indicator/SH.MED.BEDS.ZS - 24000000 beds * 4 wheels + assume 50% have monitoring carts and IV carts so 12000000 * 2 wheels = 120M

Garbage cans or other house hold bins like wagons - 2.3B homes is global estimate, drop that down to 1B to account for small homes, communal living, old trash cans, etc. * 2 wheels = 2B.

Baby strollers, 40% of households are parents in US. Likely same in Cad, Aus, EU, UK. Either has an infant or stroller in storage. 4 wheels * households = 1.556B wheels

Trains - 1.6M freight railcars * 8 wheels. = 12.8M wheels.

Drawers - 8 rollers per drawer, assume every home has 2 desk w/ 2 drawers. + 4 drwers in kitchens.  Assume 80% of Americans work deskjobs and therefore have an office desk too, assume 1 drawer. Assume the same for entire global west+developed asia 2b people = 12.4B + 12.4B + 12.8B = 37.2B

49.09474704B + 20% for missed categories + 20% for rounding


**Estimate:**
**68.72B~**


Note to self things like below are trivial in volume by comparison captured in rounding:
airblanes
golf carts
mine cart
scooter
rollercoaster
pet wheels