---
title: "Humidity and mould risk checker | Home Comfort Lab"
description: "Enter your room temperature and humidity to see your mould risk and the temperature at which walls and windows start to get wet."
url: https://homecomfortlab.co.uk/tools/humidity-mould-risk-checker/
---

# Humidity and mould risk checker

Enter your room temperature and humidity to see your mould risk and the temperature at which walls and windows start to get wet.

By [Pete Harvey](https://homecomfortlab.co.uk/about/), editor. Updated 14 October 2026.

*This part of the page is an interactive tool. Open https://homecomfortlab.co.uk/tools/humidity-mould-risk-checker/ in a browser to use it.*

## Mould risk temperature at a glance

Each figure is the surface temperature below which mould can grow, for a room at that temperature and humidity. If your coldest wall, window reveal or corner is below it, that is where mould will appear first.

| Humidity | Room at 16°C | Room at 18°C | Room at 20°C | Room at 22°C |
| --- | --- | --- | --- | --- |
| 50% | 8.8°C | 10.7°C | 12.6°C | 14.5°C |
| 55% | 10.3°C | 12.2°C | 14.1°C | 16.0°C |
| 60% | 11.6°C | 13.5°C | 15.4°C | 17.4°C |
| 65% | 12.8°C | 14.7°C | 16.7°C | 18.6°C |
| 70% | 13.9°C | 15.9°C | 17.9°C | 19.8°C |
| 75% | 15.0°C | 17.0°C | 19.0°C | 20.9°C |
| 80% | The whole room | The whole room | The whole room | The whole room |

## Why the wall temperature matters more than the room

Mould doesn't need the whole room to be wet. It needs a surface where the air stays very humid for days at a time. The air right next to a cold outside wall, a window reveal or the back of a wardrobe is cooler than the middle of the room, and cooler air at the same moisture level has a higher relative humidity.

So a room that reads 65% on a hygrometer, only a little above the comfortable range, can still have a corner sitting above 80%, which is where mould starts. The checker shows the surface temperature at which that happens. If your coldest walls are below it, that is where mould will appear first.

## Bringing the humidity down

- Ventilate after the things that add the most water: showers, cooking and drying washing.
- Keep a low, steady background heat rather than letting rooms go very cold between bursts of heating.
- Move furniture a few centimetres off outside walls so air can reach them.
- If it stays above 60% with all of that in place, a [dehumidifier](https://homecomfortlab.co.uk/tools/dehumidifier-size-calculator/) is the next step.

More on [the ideal humidity for a UK home](https://homecomfortlab.co.uk/damp/ideal-indoor-humidity/), and on [choosing a hygrometer](https://homecomfortlab.co.uk/damp/best-hygrometer/) to measure it.

## Read next

- [What is the ideal humidity in a UK home?](https://homecomfortlab.co.uk/damp/ideal-indoor-humidity/) (How to)
  The humidity range that keeps a home comfortable and mould-free, and how to measure and control it.
- [What is a hygrometer, and which one should you buy?](https://homecomfortlab.co.uk/damp/best-hygrometer/) (Buying guide)
  A hygrometer measures how damp the air is, so you can act before mould appears. What it tells you, where to get one, and which to buy.
- [Why are my windows wet every morning?](https://homecomfortlab.co.uk/damp/why-are-my-windows-wet-every-morning/) (How to)
  Morning condensation means warm, moist air is meeting cold glass. What causes it and how to stop it.
- [What size dehumidifier do I need?](https://homecomfortlab.co.uk/tools/dehumidifier-size-calculator/) (Calculator)
  Answer four questions about your home and get the dehumidifier size and type that suits it, with what it will cost to run.

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Running costs use 26.32p per kWh for electricity and 7.97p per kWh for gas, the [Ofgem price cap, Direct Debit average for England, Scotland and Wales](https://ofgem.gov.uk/news/changes-energy-price-cap-between-1-october-and-31-december-2026) for 1 October to 31 December 2026.