# Estimation Challenge: Ranges, Not Guesses

> Teams estimate ten tricky quantities with a range they are 80 percent sure about, then discover how well calibrated they are. Duration: 30 minutes. Group size: 4–200 people. Setting: Virtual. Below you will find a step-by-step guide, the materials and facilitator tips.

URL: https://www.bravodays.com/en/team-building-library/estimation-challenge
Last updated: 2026-10-21
Publisher: BravoDays (https://www.bravodays.com)

## Key facts

- **Duration:** 30 minutes
- **Group size:** 4–200 people
- **Setting:** Virtual
- **Energy level:** Calm
- **Materials:** A list of ten questions with known answers (for example the length of a river, the population of a city, a figure from your industry), Answer sheets, A pen per team
- **Price:** Free, no sign-up

## Objective

Practise estimating with honest ranges and recognise overconfidence in forecasts.

## Materials

- A list of ten questions with known answers (for example the length of a river, the population of a city, a figure from your industry)
- Answer sheets
- A pen per team

## Step by step

1. Explain the rule: for each question, give a low and high number so that you are 80 percent sure the true answer lies between them.
2. Teams of three to five work through the ten questions in 15 minutes.
3. Reveal the answers one by one; teams count how many fall inside their ranges.
4. A well-calibrated team should get about eight out of ten; discuss whether your ranges were too narrow or too wide, and why.
5. Introduce two techniques: start from a similar known number, and break the question into parts.
6. Run a second set of five questions and compare results.

## Facilitator tips

- Make it clear that wide ranges are allowed; the goal is honesty, not precision.
- Link the debrief to real estimates at work: sales forecasts, project durations and budgets.

## Related pages

- [Team building library](https://www.bravodays.com/en/team-building-library)
- [Get a quote](https://www.bravodays.com/en/get-a-quote)