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Free tool

Air Conditioner Sizing Calculator

Enter your room sizes and get a recommended system size in seconds — split system, multi-split or ducted. Built on the same capacity rules installers use for first estimates.

2-minute guide

How to Measure a Room for Air Conditioning

1. Grab a tape measure (or your phone). Most phones have a measuring app, or pace it out — an average stride is roughly 0.8m for a rough first pass.

2. Measure length and width at floor level in metres, wall to wall. Multiply them: a 5m × 4m room = 20m².

3. L-shaped or odd rooms: split the space into rectangles, calculate each, and add them together.

4. Open-plan counts as one space. If your kitchen flows into the living room with no door, the air does too — measure the whole connected area.

5. Note your ceiling height. Standard is 2.4m; if your ceilings feel tall, they're probably 2.7m+ and you'll need extra capacity (the calculator handles this).

6. Note the sun. West-facing rooms with big windows cop the afternoon heat and need ~15% more capacity — there's a toggle per room above.

LENGTH (m) WIDTH (m) WINDOW L × W = m²

Sizing Calculator FAQs

What size air conditioner do I need per square metre?
As a rule of thumb, allow roughly 130–150 watts of capacity per square metre of floor area for a standard 2.4m ceiling — so a 20m² bedroom needs around 2.5kW and a 50m² living area around 6–7kW. Sun exposure, ceiling height and insulation shift the number, which is what this calculator adjusts for.
How do I measure my room for air conditioning?
Measure the room's length and width in metres at floor level and multiply them for the area. For L-shaped or open-plan spaces, split the space into rectangles, calculate each, and add them together. Include any connected open-plan areas air will flow into — a kitchen open to the living room counts.
Is it bad to oversize an air conditioner?
Yes. An oversized unit reaches temperature too quickly, shuts off before dehumidifying properly, then restarts repeatedly — known as short-cycling. It wears the compressor, leaves rooms clammy, and wastes power. Size correctly rather than 'going one up to be safe'.
Does ceiling height change what size I need?
Significantly. Sizing rules assume a standard 2.4m ceiling. At 2.7m add roughly 10% capacity, and at 3m or higher add around 20%, because you're conditioning the room's volume, not just its floor area.
Is this calculator a substitute for a professional heat-load calculation?
No — it's an accurate first estimate using industry rules of thumb. Your accredited installer performs a full heat-load assessment (windows, orientation, insulation, occupancy) as part of any rebate quote, which may fine-tune the size up or down.

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