---
title: "Dehumidifier size calculator: what size do I need? (UK)"
description: "Answer four questions about your home and get the dehumidifier size and type that suits it, with what it will cost to run."
url: https://homecomfortlab.co.uk/tools/dehumidifier-size-calculator/
---

# What size dehumidifier do I need?

Answer four questions about your home and get the dehumidifier size and type that suits it, with what it will cost to run.

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

This page links to Amazon. As an Amazon Associate I earn from qualifying purchases. [More about how this site is paid for](https://homecomfortlab.co.uk/affiliate-disclosure/).

*This part of the page is an interactive tool. Open https://homecomfortlab.co.uk/tools/dehumidifier-size-calculator/ in a browser to use it.*

## Dehumidifier size by home, at a glance

These tables use the same rules as the calculator. Sizes are in litres a day. If you dry washing indoors, go one size up from the figure shown.

### Heated home, 15°C or more: compressor model

| Home | Wet windows | Damp patches or musty smell | Mould or wet walls |
| --- | --- | --- | --- |
| One room | 10 | 12 | 16 |
| 1 to 2 bed flat | 10 | 12 | 16 |
| 2 to 3 bed house | 12 | 16 | 20 |
| 4 bed or more | 20 | 25 | 25, or two smaller units |

### Room often below 15°C, or unheated: desiccant model

| Home | Wet windows | Damp patches or musty smell | Mould or wet walls |
| --- | --- | --- | --- |
| One room | 7 | 8 | 10 |
| 1 to 2 bed flat | 7 | 8 | 10 |
| 2 to 3 bed house | 8 | 10 | 10, or two smaller units |
| 4 bed or more | 10 | 10, or two smaller units | 10, or two smaller units |

## What the size means

Dehumidifiers are sold by how many litres of water they can pull out of the air in a day. That figure is measured in the maker's test conditions, usually warmer and more humid than a UK home in winter, so in a normal home a 12 litre model will collect a lot less than 12 litres. That is why the calculator starts from your home's size and steps up for damp, mould and laundry rather than trying to match litres to the water you think you have.

Buying a size up is rarely wasted. A bigger unit reaches a dry room sooner, then its humidistat switches it off, so it doesn't cost much more to run than a smaller one working flat out.

## Compressor or desiccant

Compressor dehumidifiers work like a small fridge: air passes over a cold coil and the water condenses out. They use little power, but the coil struggles once the room is below about 15°C. Desiccant models soak water up with an absorbent wheel and use a heater to dry it out, so they keep working in the cold but use more electricity, and they warm the room slightly as they go.

[Compressor vs desiccant in more detail](https://homecomfortlab.co.uk/damp/compressor-vs-desiccant-dehumidifier/).

> **When a dehumidifier isn't the fix**
>
> If damp appears after rain, sits in a band low on a wall, or comes from a leak, a dehumidifier only treats the symptom. [Check which type of damp you have](https://homecomfortlab.co.uk/damp/condensation-vs-rising-damp-vs-penetrating-damp/) first.

## Read next

- [Compressor vs desiccant dehumidifier: which do you need?](https://homecomfortlab.co.uk/damp/compressor-vs-desiccant-dehumidifier/) (Buying guide)
  Compressor models are cheaper to run in a heated home; desiccant models work better in cold rooms. How to choose.
- [Dehumidifier running costs: popular models compared](https://homecomfortlab.co.uk/damp/dehumidifier-running-costs/) (Running costs)
  What each popular dehumidifier costs per hour and per month at the current price cap, from its rated power.
- [Best dehumidifier for drying laundry](https://homecomfortlab.co.uk/damp/best-dehumidifier-for-drying-laundry/) (Buying guide)
  What makes a dehumidifier good at drying clothes, and the models whose specs suit it best.
- [Appliance running cost calculator](https://homecomfortlab.co.uk/tools/running-cost-calculator/) (Calculator)
  Find out what any electric appliance costs per hour, day, month and winter at the current UK price cap.

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As an Amazon Associate I earn from qualifying purchases. Links to shops are marked, and earning from them never decides what we recommend. [How this site is paid for](https://homecomfortlab.co.uk/affiliate-disclosure/).

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.