Guesstimate

What a typical guesstimate looks like

Most Guesstimates require you to make an estimate of the number of people that would purchase a product/service and the footfall of particular locations or events. Guesstimates require you to be analytical, logical and concise. It is a type of question asked not just in case interviews but also in interviews as this is an indicator of your creativity and problem solving ability.

Guesstimates can be asked in 2 ways. As a standalone estimate or as part of a market entry case. Keep in mind, it is not the final answer, but how you reach your final answer that matters.

Important questions you can ask before you begin:

1. 1Over what time period and in which location am I estimating this amount
2. 2If you are estimating market size, clarify if you need to estimate it in terms of units sold or revenue generated
3. 3Clarify the industry and price point in case you are unfamiliar to better arrive at the final answer

Note: To make things easier for you, ask the interviewer if you can assume a standard size product for the purpose of this case. For e.g. in the washing machine example, there are numerous price ranges and types of washing machines sold in India. Accounting for all of this would become really hard. Hence, assume an average price and a standard size washing machine to be the only type sold.

There are two ways to begin a guesstimate - Demand-side or Supply-side.

Demand Side

As the name suggests, you aim to estimate the total demand for the product/service assuming there are no supply side constraints. The starting point of most demand side approaches is the total population that have access to the product/service. Using various parameters, you eliminate parts of the population to arrive at your final answer.

Parameters you can use while arriving at your estimate -

Supply Side

This method is generally preferred when you have a bottleneck i.e. supply side constraint. For e.g. Number of Burgers sold in McDonald's Outlet in CP. No matter what the demand is, the store can not make more number of burgers than its maximum capacity and hence there is a supply side constraint. Hence, we use the supply side approach.

Important parameters you can use in supply side approaches -

Note: Keep in mind, it is incredibly important to correctly identify whether to approach the problem through supply or demand side. An intuition that becomes better with more and more practice.

Physical Estimation

In addition to market sizing guesstimates, cases related to physical estimation are also commonly asked. In these cases, the candidate would typically be required to estimate volumes, lengths, speeds, etc.

In physical estimation, making an approximation might seem even more abstract at first. To solve this, you must use known or accurately measurable proxies to arrive at the overall figures. For instance, to estimate the size of an Airbus A320, you can consider the approximate size of a seat (based on your own body measurements) and extrapolate the size of the passenger cabin and then factor in other spaces such as the cockpit, luggage compartments and aisles.

Some important sets of formulae and data which you would require in such cases -

Guesstimate Cheat Sheet

Note: India's population can be approximately taken as 147 crores. Do familiarize yourself with facts relating to your home state, hometown and college location. Ask the interviewer if your estimates are reasonable before proceeding. These are approximated estimates as of June, 2026.