Have you heard of Butterfly Books? It is a bookstore tucked away in the bustling Worli area of Mumbai. When I visited it last Saturday, it also had the most enthusiastic buyers of books I have ever seen. Because this is a bookstore with a difference. It sells books by weight. Unlike regular bookstores where you purchase books by their cover price, Butterfly Books has created a unique offer for its customers. You can buy books of regular fiction at ₹100 per kilogram, classic literature at ₹200 per kilogram, and premium coffee table books at ₹300 per kilogram. In this premium category are included art, cookery, travel, health, academic and astrology books.

Tonnes of books This bookstore is huge. When I was there, it was packed with customers who were happily and busily picking up tonnes of books. My wife eagerly picked up several books of fiction. I found an unusual coffee table book on the Third Reich. We were then asked to take all these books to a weighing scale. We found that we had bought nearly two kilos of books, and paid for them. Now, that’s a lot more books than we would ever have bought at a regular bookstore, even if a good discount had been offered.

Other customers there were equally hungry for books. I saw a serious-looking woman picking up at least ten books by Thomas Hardy, and a thick leather-bound book of Shakespeare’s plays. I wonder how many kilos that was. Two teenage girls were busy dropping books into their shopping basket, and I could see them whooping with joy each time they found an appealing title. A bearded young fellow was busy picking up many Manga comics. He later told me that he was a writer, from Pune. He had come all the way to Worli, to buy these books by weight.

All this goes to show how greatly the concept of “books by weight” has appealed to diverse sets of consumers. I was drawn by the sheer novelty of the concept. My wife says she came along because she thought that books sold by weight would be part of a clearance sale, and therefore excellent value for money. The young fellow buying Manga comics came because he thought comics were generally quite light in weight, so they would cost far less when sold by grammage.

Matters of weight Butterfly Books was doing very brisk business. This led me to think – are there other categories which have used the concept of weight in interesting ways? All of us are accustomed to buying our groceries and vegetables by weight, but are there other products where weight is not the natural unit of measurement, but is still deliberately used to evoke consumer interest and demand? And in each of these cases, what does the use of “weight” really mean?

The first such category which comes to mind is gold jewellery. In most western countries, gold jewellery is not sold by weight, but by a fixed price per piece of jewellery. In India, however, weight is regarded by consumers as the primary unit of measurement for this category, because for Indian women, gold jewellery is both adornment and future value (investment). Weight of the gold is the key determinant of future value, and hence critical.

At restaurants Unlike books by weight, which may signal a clearance sale, there are other categories where weight signals preciousness or rarity. For instance, in seafood restaurants in Mumbai, most of the regular dishes (such as fish curry) are available at a fixed price on the menu. However, lobster is generally sold by weight – which signals the rarity of this dish. Typically, the restaurant will tell you the cost of lobster per hundred grams, and you then decide how much you wish to order. Caviar, which is considered a luxury, is also similarly presented by weight, wherever it is available. The cost of these indulgent items is quoted not in kilograms but in grams – which further emphasises their preciousness.

Quite in contrast to this are some restaurants where buffet meals are sold by weight. So you have the example of a café in Delhi, which offers consumers a system of “weigh and pay”. It charges ₹18 per 100 gm of vegetarian food, and ₹28 per 100 gm of non-vegetarian food. Consumers can choose any combination of dishes they wish to, from the buffet, and then they pay by overall weight. In this case, payment by weight does not signal preciousness or a clearance sale. On the other hand, it leads consumers to prudent decision-making, to choosing exactly the amount of food they can eat, without any wastage of either food or money, and the associated guilt.

Consumers can therefore feel good that they have bought exactly what they require. Incidentally, an interesting survey at this restaurant has revealed that, on average, people eat 300 gm of food at a single meal, but very hungry people eat up to 450 gm or even more.

A very different concept of food by weight can be found in some restaurants that sell desserts only by weight. After a fulfilling meal, you can buy exactly 50 gm of tiramisu or even 25 measly grams of sinful chocolate cake. Here, weight signals calorie control, because you can eat a strictly measured portion of your choice – rather than dig greedily into a standard helping of pudding with zillions of calories in it. If many of you are dining together, each of you has the flexibility to choose your own weight of dessert. So you can enjoy your dessert, and still keep your diet and waistline intact.

Airlines and weight Let’s move on to the interesting concept of flying by weight. We are accustomed to paying per seat, whenever we fly. But here is an airline which does things differently. Samoa Airlines, the Pacific National Airline, is the world’s first airline to charge passengers by weight. Passengers do not pay for a seat, but pay a fixed price per kilogram of their body weight, and this fixed price varies by length of the route. Flying by this arline costs $1 per kg on the shortest domestic route, and up to $4.2 for travel from Samoa to neighbouring nations. In fact, Samoa Airlines uses the advertising byline “Where you pay by weight”.

Many consumers, particularly those who are slim or tiny, and who have got uncomfortably wedged between rather heavy passengers on flights, may feel that this is quite a fair method of pricing. After all, aircraft can carry only a limited amount of weight, so why not charge passengers by their weight?

In due course, such pricing may lead to natural segmentation – passengers who are lighter will more likely choose airlines which charge by weight, and passengers who are heavier will perhaps be happier with the conventional price per seat.

This exploration opens up interesting possibilities. Can gymnasiums charge consumers by the amount of weight they lose, in addition to a fixed monthly fee? Alternatively, can gymnasiums take a cash deposit to begin with, which they can then refund to consumers for every kg of weight lost? This may create a natural incentive for people to work out. Can Uber or Ola taxis introduce weight-based pricing for their passengers, or would this be considered discriminatory? Can hair styling salons introduce haircuts by weight? Can jeans or leather jackets or carpets or laptop computers be sold by weight? At a broader level, can this conversation move beyond weight, to include the appropriate use of non-conventional units such as length, height, density or space, to generate new streams of consumer interest in various products and services? All these questions offer marketers many kilograms of food for thought.

(Harish Bhat is Member, Group Executive Council, Tata Sons. He is the author of Tata Log: Eight modern stories from a timeless institution”. These are his personal views. )