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The Virus Tool to estimate the viral dose in rooms

A guide towards healthy classrooms

Virus Tool

Update: There is a new version (v2.2) with CO2 calculator and recirculation of purified virus-free air.

The Indoor Scenario Simulator for COVID-19 was developed with financial support from the State Secretariat for Economic Affairs SECO ( and in cooperation with Christian Monn, SECO. The update was financed by internal SCOEH funds.

Download version 2 (English): The Tool (spreadsheet), User Guide (PDF)

Runterladen von Version 2 (Deutsch): Das Tool (Tabelle), Anleitung (PDF)

Descargar (Español): herramienta de virus (hoja de cálculo), Guía corta (PDF)

Scarica versione 2 (Italiano): Lo Strumento (Foglio di calcolo), Guida rapida (PDF)

Télécharger version 2 (Français) : L’outil (tableau), Guide rapide (PDF)

下載繁體中文第二版 :  工具(工作清單)使用說明手冊(PDF檔)

ダウンロード (日本語版)

This tool calculates the concentration of viruses in a room with perfect mixing for one or more people who emit viruses while breathing normally, speaking softly or loudly. The new version addresses the fact that there are much higher viral loads in the population with the new virus variants. A “person with high virus emission” is now the normal case (median) and the presence of a super-emitter is a quite realistic assumption in many scenarios.

The tool allows the calculation of scenarios where virus carriers enter a room, stay there for a certain time, and what this means for exposure and inhaled dose from other people in the room. The new version also allows the simulation of air purification by means of air circulation (e.g. by mobile air filter units equipped with highly efficient particle filters or physical air disinfection). In addition to virus counts, the new version also provides an estimate of CO2 levels. Graphs now show the time course of virus dose and CO2 levels in the room.

A detailed description of the initial tool can be found in the blog. The underlying scientific article can be found in the scientific magazine Aerosol and Air Quality Research. The initial version of the tool can be downloaded here.

This tool was created with great care and checked in detail, but may contain errors. DO NOT use the tool as the sole element for critical decisions.

The tool is free of charge and made available under the Creatives Commons Attribution License 4.0 (CC BY 4.0).

Guide towards healthy classrooms

This tool provides guidance on how to assess and define ventilation strategies to reduce the potential spread of the SARS-CoV-2 virus through aerosol transmission in classrooms.

The guide explains how to check if the ventilation is sufficient to reduce the risk of transmission by aerosols. We use CO2 as a tracer gas since this is already emitted by the people in the room. The guide also describes the risk of infection under different scenarios in a classroom. 

The guide can be applied to other types of indoor spaces, such as offices or other public buildings, though some adjustments may be needed for physical characteristics (e.g. area and volume). 

The guide focuses on ventilation in classrooms, alongside tools to evaluate the implemented ventilation strategies. The use of masks, maintaining physical distance, and upholding hygiene measures, must be adhered to in conjunction with the strategies described in the guide.

This guide was developed by researchers from Europe’s COST-Action INDAIRPOLLNET (led by Xavier Querol and Maricruz Minguillón from CSICand Michael Riediker from SCOEH).

The measures described aim to reduce the risk of contagion, but they do not eliminate the risk entirely.


  1. The guide (PDF)
  2. Spreadsheet File (Excel) to calculate how well a room is ventilated (requires CO2-measurements)
  3. The Indoor Scenario Simulator

The guide is also available at CSIC.

The guide is free of charge and comes without a specific license. Feel free to copy it into your language. Please attribute the source and the work of INDAIRPOLLNET when using it.