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How Many BTU Do I Need for My Split AC? Calculator by m²

Enter your room size and climate zone and get the exact BTU your split AC needs, plus the frigorías equivalent. Formula: BTU = m² × climate factor (600–850 BTU/m²).

Data verified · June 2026
Edited by Martín Rodríguez
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This calculator determines the correct BTU (British Thermal Unit) capacity needed for a split air conditioner based on your room's square footage and local climate. BTU is the standard unit measuring how much heat an AC unit can remove per hour. The core formula is: BTU = Room Area (m²) × Climate Factor (BTU/m²). Climate factors range from 600 BTU/m² in mild zones to 850+ BTU/m² in hot/humid regions. Getting this right is critical: an undersized unit runs non-stop and never cools properly, while an oversized unit short-cycles, leaving the air humid and uncomfortable.

When to use this calculator

Choosing the right split AC unit before purchase for a 15 m² bedroom in a hot climate
Sizing a mini-split for a converted garage of 40 m² with poor insulation and direct sun exposure
Replacing an old window unit with a ductless split in a 25 m² living room to reduce electricity bills
Calculating cooling needs for a home office in a temperate climate where summer peaks occur
Verifying that a landlord-installed 9,000 BTU split is actually sufficient for a 22 m² apartment room in a warm climate

BTU to Commercial Split AC Size Reference

BTU Range	Frigorías (kcal/h)	Commercial Label	Nominal Tons
7,000–9,000	1,764–2,268	9,000 BTU	0.75 ton
9,001–12,000	2,268–3,024	12,000 BTU	1 ton
12,001–14,000	3,024–3,528	14,000 BTU	1 ton+
14,001–18,000	3,528–4,536	18,000 BTU	1.5 ton
18,001–24,000	4,536–6,048	24,000 BTU	2 ton
24,001–30,000	6,048–7,560	30,000 BTU	2.5 ton
30,001–36,000	7,560–9,072	36,000 BTU	3 ton

Fuente: ENERGY STAR / ASHRAE Manual J — Conversion: 1 BTU/h = 0.252 frigorías (kcal/h). Always round up to the next available commercial size.

How it works

How It's Calculated

The fundamental formula used by HVAC engineers and endorsed by ENERGY STAR guidelines is:

BTU/h = Room Area (m²) × Climate Factor (BTU/m²)
Frigorías (kcal/h) = BTU/h × 0.252

Example:
  Room = 20 m², Warm climate (Factor = 700)
  BTU/h = 20 × 700 = 14,000 BTU/h
  Frigorías = 14,000 × 0.252 = 3,528 kcal/h
  → Select: 14,000–18,000 BTU split

The climate factor captures the combined effect of outdoor temperature, solar gain, humidity, and typical insulation levels for each zone. The DOE's Manual J methodology uses similar load calculations; this formula is a practical approximation widely used for residential split AC sizing.

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BTU Chart by Room Size and Climate

Room Size (m²)	Temperate (600)	Warm (700)	Very Hot (850)	Recommended Split
10	6,000 BTU	7,000 BTU	8,500 BTU	9,000 BTU / 0.75 ton
15	9,000 BTU	10,500 BTU	12,750 BTU	12,000 BTU / 1 ton
20	12,000 BTU	14,000 BTU	17,000 BTU	12,000–18,000 BTU / 1–1.5 ton
25	15,000 BTU	17,500 BTU	21,250 BTU	18,000 BTU / 1.5 ton
30	18,000 BTU	21,000 BTU	25,500 BTU	24,000 BTU / 2 ton
40	24,000 BTU	28,000 BTU	34,000 BTU	30,000–36,000 BTU / 2.5–3 ton
50	30,000 BTU	35,000 BTU	42,500 BTU	36,000–48,000 BTU / 3–4 ton

> Always round up to the next available commercial size — never down.

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Climate Factor by Zone

Climate Type	Typical Regions	BTU per m²
Temperate	Northern Europe, Pacific Northwest, NZ	500–600
Warm	Mediterranean, Southeast US, Northern Argentina	600–700
Hot	South Florida, Gulf Coast, Buenos Aires summers	700–800
Very Hot & Humid	Tropical zones, Corrientes AR, Puerto Rico	800–850
Hot & Dry	Phoenix AZ, Las Vegas NV, desert zones	850–950

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BTU to Commercial Split AC Sizes

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Common Mistakes

1. Ignoring ceiling height. The base formula assumes a standard 2.5 m (8 ft) ceiling. Rooms taller than 3 m need a volume correction: multiply BTU result by (actual ceiling height ÷ 2.5).

2. Not accounting for sun exposure. South- and west-facing rooms with large glass windows can receive 400–600 W/m² of solar gain. Add 10–15% to the BTU result for heavy sun exposure rooms.

3. Choosing the smallest unit to save money. An undersized split runs at 100% capacity continuously, wears out faster, and never reaches the setpoint temperature.

4. Ignoring internal heat sources. Each person in a room adds ~250–400 BTU/h. A kitchen adds 4,000+ BTU/h from cooking. Offices with multiple computers can add 1,000–3,000 BTU/h of load.

5. Oversizing the unit. An oversized unit short-cycles — it reaches the setpoint quickly and shuts off before removing enough moisture. This leaves the room cold but clammy.

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Worked Example

Room: 20 m², warm climate (factor = 700 BTU/m²)

BTU = 20 × 700 = 14,000 BTU/h

Frigorías = 14,000 × 0.252 = 3,528 kcal/h

Select a 3,500F (14,000–18,000 BTU) split — next commercial size up

Frequently asked questions

How many BTU do I need for a 20 m² (215 sq ft) room?

In a warm climate: 20 m² × 700 BTU/m² = 14,000 BTU/h (3,528 frigorías). In a temperate climate: 20 × 600 = 12,000 BTU/h. The closest commercial split sizes are 12,000 BTU (1 ton) or 18,000 BTU (1.5 ton) — choose based on whether your climate factor result is above or below the midpoint.

How many BTU per square meter do I need?

600 BTU/m² for temperate climates (Pacific Northwest, northern Europe), 700 BTU/m² for warm climates (Mediterranean, southern US, Argentina), and 850 BTU/m² for very hot/humid zones (tropical regions, Gulf Coast, desert). These factors align with the DOE Manual J approach and ENERGY STAR guidance.

What is the difference between BTU and frigorías (kcal/h)?

Both measure cooling power in different unit systems. 1 BTU/h = 0.252 kcal/h, so 1 frigoría = 1 kcal/h ≈ 3.968 BTU/h. In Latin America and parts of Europe, split AC units are rated in frigorías. A 12,000 BTU unit equals roughly 3,024 frigorías.

Should I choose a fixed-speed or inverter split AC?

For most residential applications, an inverter (variable-speed) compressor is strongly preferred. Inverter units modulate output between ~30–100% of rated capacity, saving 25–40% in electricity vs. fixed-speed units per ENERGY STAR data. They also maintain more stable temperatures and have longer compressor life.

How do I convert BTU to tons of refrigeration?

1 ton of refrigeration = 12,000 BTU/h. So a 24,000 BTU split = 2 tons; an 18,000 BTU split = 1.5 tons. This ton-based naming is standard in the US HVAC industry and on most equipment spec sheets.

Does the BTU formula change for a kitchen?

Yes. Kitchens have major internal heat loads from cooking appliances. Add 4,000–6,000 BTU/h for a residential kitchen with a gas or electric range. So a 15 m² kitchen in a warm climate: (15 × 700) + 5,000 = 10,500 + 5,000 = 15,500 BTU/h → select an 18,000 BTU unit instead of the 12,000 BTU you'd use for a bedroom of the same size.

What happens if I install a split AC that is too large (oversized)?

An oversized unit short-cycles — it reaches the thermostat setpoint very quickly and shuts off before removing enough moisture from the air. This leaves the room feeling cold but clammy. The frequent on-off cycles also stress the compressor, reducing lifespan. ENERGY STAR specifically warns against oversizing; the goal is to size within 15% of the calculated load.

Can I use one large split AC to cool multiple rooms?

A single-zone split AC cools only the room where the indoor unit is installed. Adjacent rooms rely on air circulation through open doors, which is inefficient and uneven. For multi-room cooling, a multi-zone (multi-split) system connects 2–5 indoor units to one outdoor compressor. Each indoor zone should be sized independently.

What is SEER2 and why does it matter?

SEER2 (Seasonal Energy Efficiency Ratio 2) is the updated DOE efficiency metric. It measures total cooling output (BTU) divided by total electrical energy used (Wh) over a cooling season. The US federal minimum for split systems ≤45,000 BTU is SEER2 13.4. Higher SEER2 = lower electricity bills; top units reach SEER2 20–26.

Sources & references

Methodology & trust

Editorial

Construction calculator with its formula verified automatically against ENERGY STAR — Room Air Conditioner Key Product Criteria, per our editorial policy and methodology.

Updates

Updated: June 2026. Parameters are verified periodically against the cited sources.

Privacy

Calculations run 100% in your browser. We do not store or transmit your data.

Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

Rodríguez, M. (2026). How Many BTU Do I Need for My Split AC? Calculator by m². Hacé Cuentas. https://hacecuentas.com/en/split-ac-btu-calculator

Content licensed under CC-BY 4.0 — reuse it citing the source with a link to Hacé Cuentas.

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