The right air conditioning capacity depends on the size of your space, the insulation, and factors such as sun exposure and glass surface area.

• Calculate on average with 30–40 Watts per m³ or 60–100 Watts per m².

• 1 kW = 3,410 BTU/h.

• For an average room of 25 m², you end up with 2.1 to 2.6 kW cooling capacity.
  In doubt? Choose slightly more rather than too little — but avoid oversizing.

At the bottom of this article 

Buying an air conditioner starts with one important question: how much capacity do you actually need?

Too little capacity means your space will not be cooled properly. Too much capacity leads to unnecessary energy consumption, higher costs, and a less stable indoor climate.

In this article, we clearly explain:

• The difference between electrical power and cooling capacity

• How to calculate the required capacity yourself

• Which factors really influence it

• How to determine the correct insulation class

Electrical power vs. cooling capacity: this is the difference

These are often confused, but they are not the same.

• Cooling capacity (kW) → how much heat the air conditioner removes from the space

• Electrical power (kW) → what the air conditioner consumes from the power outlet

So the cooling capacity determines whether your space becomes comfortably cool.

kW and BTU: how does that work?

The cooling capacity of an air conditioner is expressed in:

• kW (kilowatt)

• or BTU per hour (BTU/h)

The conversion is simple:

1 kW = 1,000 Watts = 3,410 BTU/h

Example:
An air conditioner of 2.5 kW has approximately 8,525 BTU/h cooling capacity.

Method 1: Calculate via floor area (m²)

A quick and practical method is to calculate per square metre.

Formula:

Cooling capacity (W) ≈ floor area (m²) × 60–100

Guidelines per situation:

• 60–70 W/m² → well insulated, little sun (new build, north side)

• 80–90 W/m² → average (most common in the Netherlands)

• 100 W/m² or more → lots of glass, lots of sun, attic, moderate insulation

Example

A living room of 25 m², moderately insulated:

25 × 85 W = 2,125 Watts ≈ 2.1 kW

Method 2: Calculate via room volume (m³)

Want to calculate more accurately? Use the volume of the room.

Step 1: Calculate the volume

Volume (m³) = m² × ceiling height

Example:
25 m² × 2.6 m height = 65 m³

Step 2: Multiply by the correct factor

Cooling capacity (W) ≈ volume (m³) × 25–60 W

Guidelines:

• 25–35 W/m³ → well insulated / little sun

• 35–45 W/m³ → average

• 45–60 W/m³ → lots of sun / attic / moderate insulation

Example calculation

65 m³ × 40 W = 2,600 W = 2.6 kW

-- This is more realistic than just calculating per m².

Additional factors that influence the required capacity

Besides area and volume, these factors play a major role:

• Insulation value of walls, roof and windows

• How much glass surface the room has

• Orientation relative to the sun (south vs. north)

• Type of room (attic warms up faster than living room)

• Layout of the room (L-shape, open stairwell)

• Internal heat sources (equipment, kitchen, multiple people)

Important: do not underestimate sun exposure. A south-facing room with lots of glass often requires 15–25% more capacity.

Insulation classes: which category does your room fall into?

As a rule of thumb for an average house in the Netherlands:

30–40 Watts per m³
(≈ 100–135 BTU per m³)

But to determine more accurately what you need, you can classify your room into an insulation class.

The higher the class, the more capacity you need. Use this table + the image below to make a good estimate! 

What happens with incorrect sizing?

Too little capacity:

• Room does not get cool enough

• Air conditioner runs continuously at maximum power

• Higher wear and tear

Too much capacity:

• Rapid cooling without dehumidification

• Uncomfortable temperature fluctuations

• Unnecessarily high purchase costs

A correct calculation thus ensures:
✔ Comfort
✔ Lower energy consumption
✔ Longer lifespan

Practical overview

For a standard ceiling height of 2.6 metres:

Note: this remains a guideline, use the methods above to determine more accurately how much capacity you need. 

Conclusion: how many kW air conditioner do you need?

Most living spaces in the Netherlands fall between 2.0 and 5.0 kW cooling capacity.

Want to keep it simple?

• Well insulated → 30 W per m³

• Average → 40 W per m³

• Lots of sun or attic → 50+ W per m³

This way you quickly know approximately where you should be.

Need advice?

Are you unsure between 2.5 kW or 3.5 kW?
Or do you want to know which type of air conditioner best suits your situation?

👉 Check out our range of air conditioners or contact us for personal advice.

This way you are sure to choose the right capacity — and stay comfortable this summer.

Sales@4blue.nl 

Call (024) 204 20 90