Air Conditioner Size Calculator

The free Australian air conditioner size calculator — also a handy kW calculator and aircon estimator: enter your room size in square metres and get the right split system, multi-split or ducted capacity in seconds, built on the same kW-per-square-metre rules licensed installers use for first estimates.

Ceiling height

Insulation

The faint grey numbers are average Australian room sizes, shown only as a guide — your fields are still empty. Tap each box and enter your room's real length and width for an accurate result.

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.

How to Calculate Aircon Size for a Room

The formula installers start with: room area (m²) × 130 watts. Measure length × width in metres, multiply by 0.13, and you have the kW estimate — a 20m² bedroom is 20 × 0.13 = 2.6kW, so a 2.5kW unit fits. Then adjust: add ~10–20% for ceilings above 2.4m, ~15% for west-facing rooms with big windows, and ~15% for poor insulation — or skip the maths and let the calculator above apply the adjustments for you. Round up to the next standard size (2.5, 3.5, 5.0, 7.1, 8.0, 9.4kW), never down.

Quick Reference: Size by Room Type

Room	Typical size	Recommended capacity
Bedroom / study	10–20 m²	2.0 – 2.5 kW
Large bedroom / small lounge	20–30 m²	2.5 – 3.5 kW
Living room	30–45 m²	4.2 – 5.0 kW
Open-plan living/dining	45–65 m²	6.0 – 8.0 kW
Large open-plan	65–90 m²	8.5 – 9.4 kW
Whole home (ducted)	120–280 m²	10 – 20 kW zoned

Once you know your size, check what your state pays toward it: NSW rebates run $200–$2,600+, Victoria up to $5,530, and SA's REPS delivers the deepest concession discounts — or jump straight to the postcode checker.

How Many kW Do I Need?

The short answers, at a standard 2.4m ceiling and average insulation. Use the calculator above for your actual room, and round up to the next size a brand makes.

A bedroom or study (10 to 20m²): 2.5 kW. Only the biggest bedrooms with a west-facing window need 3.5 kW.
A living room (30 to 45m²): 5.0 kW, or 6.0 to 7.1 kW if it is open to the kitchen or gets afternoon sun.
A large open-plan living and dining area (45 to 65m²): 7.1 to 8.0 kW. Beyond that a single split struggles to move the air and a second unit or ducted is the better answer.
A whole house (ducted): roughly 0.1 kW per square metre of conditioned floor area with zoning, so a 3-bedroom single-storey home of 120 to 150m² sits around 12 to 14 kW, and a 4-bedroom double-storey home of 200 to 250m² around 18 to 20 kW. Ducted sizing depends on how many zones run at once, so an installer confirms it on inspection.

Multi-split systems are sized per room using the same numbers, then the outdoor unit is chosen to cover the rooms you would run together. The multi-split guide and ducted and VRF guide cover the trade-offs.

What Size Room Does Each kW Unit Cool?

The same numbers the other way round, for when you already have a unit or a quote and want to know if it fits. The first column is a comfortable maximum at a standard ceiling; the second is the stretch figure for a well-insulated, shaded room.

Unit capacity	Comfortable room size	Maximum (good insulation, no afternoon sun)
2.5 kW	up to 18 m²	20 m²
2.6 to 2.7 kW	up to 20 m²	22 m²
3.5 kW	20 to 28 m²	30 m²
4.2 kW	28 to 33 m²	36 m²
5.0 kW	33 to 40 m²	44 m²
6.0 kW	40 to 48 m²	52 m²
7.1 kW	48 to 55 m²	60 m²
8.0 kW	55 to 62 m²	68 m²
9.0 to 9.4 kW	62 to 72 m²	78 m²

Capacities are the cooling figure on the spec sheet. Every major brand makes units at or near these sizes; the Mitsubishi Electric, Daikin and Rinnai pages list the exact model capacities and the rebate on each.

Sizing Calculator FAQs

How do I calculate aircon size for a room?

Multiply the room's area in square metres by 130 watts (0.13kW). A 4m x 5m room is 20m2, so 20 x 0.13 = 2.6kW — round up to the next standard size. Add roughly 10–20% for high ceilings, 15% for west-facing sun and 15% for poor insulation, which is exactly what this calculator does automatically.

Is an aircon size calculator accurate?

As a first estimate, yes — this calculator uses the same kW-per-square-metre rules installers apply when scoping a job. Final sizing should always be confirmed by a licensed installer's heat-load assessment, which accounts for windows, orientation and construction — included free with any rebate quote.

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.

How many kW air conditioner do I need?

About 0.13 kW per square metre at a standard ceiling: 2.5 kW for a bedroom up to 18m², 3.5 kW for a large bedroom or small lounge, 5.0 kW for a 33 to 40m² living room, and 7.1 to 8.0 kW for open-plan areas up to about 60m². Add capacity for high ceilings, west-facing windows and poor insulation, then round up to the next size a brand makes.

What size room does a 5 kW air conditioner cool?

A 5.0 kW split system comfortably cools 33 to 40 square metres at a standard 2.4m ceiling, and up to about 44m² if the room is well insulated and does not get afternoon sun. That covers most Australian living rooms; open-plan living and dining areas usually need 7.1 kW or more.

How many kW ducted air conditioning do I need for a whole house?

Allow roughly 0.1 kW per square metre of conditioned floor area with zoning. A 3-bedroom single-storey home of 120 to 150m² typically needs 12 to 14 kW, and a 4-bedroom double-storey home of 200 to 250m² around 18 to 20 kW. The exact size depends on how many zones run at once and the roof space, so a ducted quote is always confirmed on inspection.

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