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Parent Topic: Forecasting

Guesstimate is a web-based spreadsheet tool built to focus on uncertainty. It's useful for fermi estimates and collaborative modelling.

External links

Guesstimate official website

Guesstimate documentation

Related Entries

Tools for Collaborative Truth Seeking | Squiggle | QURI


Video tutorial available here, text tutorial below. 

Why use guesstimate?

Guesstimate is built to focus on uncertainty. The interface works the same as google sheets or excel; a grid of cells where data can be entered. Cells can then be referenced by other cells for calculations. 

Guesstimate has two key benefits over google sheets/excel:

  1. Each cell can have uncertainty
  2. Cell references are displayed visually (as well as in the formula of a cell)

This means that guesstimate is highly appropriate for fermi estimateslogic models, and any other format where you have uncertainty about some or all of the inputs, or of their effect sizes on the outputs. The visual nature of guesstimate also makes it easy to share; it’s easy to see how a model works.

If you prefer hands-on learning, a simple model to demonstrate the basic features is available here

Basic Guesstimate Functions

Double click anywhere empty in the grid to create a new cell. A cell has two attributes, a 

name and a value. A name should just help people understand your model. The value can be of several types:

  • Single value (7000)
  • 90% Confidence interval (6 to 7)
  • Specific dataset (9.8, 17, 12, 34, -2, 113)


Cells’ value can also reference other cells like other spreadsheets. Typing ‘=’ at the beginning of the value field tells guesstimate the value is a formula; you can then click any other cell to create a reference to it, and perform basic numerical operations or ‘if’ statements on them. 

While editing a formula, cells also show a three-letter reference at their top right, which you can type to manually refer to another cell. 

For a more in-depth guide, see the official documentation