Q: How many hotel-sized bottles of shampoo and conditioner are produced each year around the world?

A: You might begin by assuming that hotel-sized bottles are produced for two purposes only:

1. To supply hotels and upscale motels

2. To provide samples for gift packs, salons, and so on

You would then want to start by estimating the number of hotels and motels around the world that offer the products to their guests. One way of estimating the number of hotels is to assume that hotels are found predominantly in major cities and resorts. Figure that there are 2,000 major cities and resorts around the world, an average of ten for each of the world’s approximately 200 countries. Assume that each city averages 20 hotels that offer bottled hair products to their guests. Multiplying 20 by 2,000 gives you 40,000 hotels around the world that require shampoo and/or conditioner for their guests.

To understand how many bottles of shampoo and conditioner the 40,000 hotels require, you now need to estimate the total number of uses each hotel on average represents. You can arrive at that number through the following calculation: assume that there are 100 rooms in each hotel, and that those rooms are occupied 50 percent of the time. Multiplying 40,000 by 100 by 0.5 by 365 (don’t forget the number of days in the year!) gives you approximately 750 million.

However, it is probably reasonable to assume that a guest staying for longer than a day will not use a whole shampoo bottle every day. If you assume that an average of one shampoo bottle is used for every two occupied days in a given room, you can now divide your 750 million estimate in half to 375 million. To get to the number of bottles of conditioner, estimate a ratio between the use of shampoo and the use of conditioner. Since many of us do not condition every time we shampoo, you might assume that the ratio is 2:1. Dividing 375 million in half gives you approximately 190 million. Your conclusion would then be that 375 million bottles of shampoo and 190 million bottles of conditioner are required for hotel use every year.

To estimate the total market size, you can probably make things easy on yourself by assuming that the number produced for sample purposes is a small percentage of the total, say ten percent. Combining your two markets would give you approximately 400 million bottles of shampoo and 210 million bottles of conditioner.

Finally, you might want to “reality check” your total figure. Assuming 610 million bottles are produced and sold each year at an average price of 25 cents each, the worldwide market for miniature bottles of shampoo and conditioner is about $150 million. Does that sound reasonable?