Air-Conditioner Sizing & Running Cost Calculator

ASEAN AIR CONDITIONING ENERGY SUSTAINABILITY

By RECATOOLS Editorial Last reviewed 2 Aug 2026

About this tool

Size the unit, then see what it really costs to run each month

Air-conditioner sizing and running-cost calculator — enter your room size, sun exposure and hours of use to get the right BTU and horsepower, then the monthly running cost and CO₂ on your own tariff. Singapore uses the NEA minimum efficiency standard of 4.86. Runs in your browser.

RT-SUS-003 · Sustainability & Environment

Room area · 14 m²

Sun exposure

Occupants

Hours per day · 8

Region

Your tariff (optional)

/ kWh

Your unit’s rated efficiency (optional)

The coefficient of performance printed on the energy label. Leave blank to use the regulated minimum for your region.

How to Use the Air-Conditioner Calculator

Enter the room

Set the floor area, choose how exposed it is to the sun, and how many people are usually in it. The gauge shows the cooling load in BTU/h.

Read the recommended size

The tool rounds the load up to the nearest standard unit and shows the horsepower class to look for.

Set hours and tariff

Enter daily running hours and your region, or your exact tariff from the bill, to get the monthly running cost and CO₂.

Sharpen it with your own unit

In Singapore, type the coefficient of performance from the model’s energy label into the efficiency field. Elsewhere, enter the inverter price premium to see how quickly the energy savings pay it back.

Sizing and Running an Air-Conditioner

Choosing an air-conditioner is really two questions: how big should it be, and what will it cost to run? Both matter more in a tropical climate than almost anywhere else, because the unit works hard for long hours all year round. This calculator tackles both. For sizing, it estimates the cooling load of your room — the amount of heat the air-conditioner has to remove every hour to keep you comfortable — and expresses it in BTU per hour, the standard unit of cooling capacity. The load grows with floor area, with sun exposure, and with the number of people in the room, since bodies, lighting and electronics all add heat. The tool applies a tropical baseline of roughly 600 BTU/h per square metre, adjusts it for how much sun the room takes, adds a margin for extra occupants, and then rounds up to the nearest standard unit size, shown in both BTU and the horsepower classes that air-conditioners are sold by across Southeast Asia.

Getting the size right is not just pedantry. An oversized unit reaches the set temperature so quickly that it switches off before it has wrung enough moisture out of the air, leaving a room that feels cold and damp, and the constant on-off cycling wastes electricity and shortens the compressor’s life. An undersized unit has the opposite problem: it runs continuously, never quite catches up on the hottest afternoons, and still costs a fortune because it never gets to rest. Matching capacity to load — neither too big nor too small — is what delivers steady comfort at the lowest running cost.

The second half of the tool turns capacity into money. It converts the unit’s cooling output into the electrical power it actually draws using a coefficient of performance — a measure of how much cooling you get per unit of electricity — then works out the monthly kilowatt-hours, cost and carbon emissions using your local electricity tariff and grid carbon factor.

Which efficiency figure it uses depends on where you are, and Singapore is now a special case worth explaining. Since 1 April 2025 the National Environment Agency has required every single-split air-conditioner up to 17.6 kW sold here to reach a coefficient of performance of at least 4.86, raised from 4.04, with a grace period for existing stock that ended on 31 March 2026. That floor applies to inverter and non-inverter models alike, although it is measured differently for each: inverters are rated on a part-load blend that weights performance at half capacity more heavily than at full, while fixed-speed units are rated at full load. The practical consequence is that the old inverter-versus-non-inverter comparison no longer has two different numbers to compare, so for Singapore this calculator shows a single running cost built on 4.86 and says so, rather than manufacturing a gap between the two types. An inverter is still very likely the cheaper machine to live with, because a fixed-speed compressor gives some of its rated efficiency back every time it stops and restarts — but no published figure says how much, and a payback period built on a guess would look far more precise than it deserves.

Two things follow from that, both of which make the estimate better rather than vaguer. First, 4.86 is a legal minimum and not an average, so the Singapore figure is an upper bound on what a new unit should cost you to run; an air-conditioner bought before the standard changed will cost more. Second, every unit sold here carries an energy label with its own rated coefficient printed on it, and typing that number into the efficiency field replaces our assumption with your machine. In markets where we have not sourced a minimum standard, the tool keeps the older side-by-side comparison on typical planning figures of 3.5 and 2.8, clearly labelled as estimates, along with the premium payback. Everything is computed in your browser from factors you can inspect in the panel below the calculator, with no data leaving your device.

The cheapest air-conditioner to run is the one that is sized correctly and then left at a sensible temperature — not the coldest or the biggest.

10 Facts About Air-Conditioning

Cooling capacity is measured in BTU per hour.

In SE Asia, 1 hp ≈ 9,000 BTU/h.

An oversized unit short-cycles and dehumidifies poorly.

An undersized unit runs flat-out and never cools.

Inverters vary compressor speed instead of on/off cycling.

Singapore’s minimum standard is COP 4.86 since April 2025.

West-facing rooms need more cooling from afternoon sun.

Each extra person adds roughly 600 BTU/h of load.

Every 1 °C lower on the thermostat raises energy use.

This calculator runs in your browser — nothing is uploaded.

Frequently Asked Questions

As a tropical rule of thumb this tool uses about 600 BTU/h per square metre for a normally-exposed room, adjusts for sun exposure, and adds roughly 600 BTU/h for each occupant beyond two. It then rounds up to the nearest standard unit size. Enter your room area and exposure and it shows the recommended BTU and horsepower.
In Southeast Asia air-conditioners are commonly sold by horsepower rather than BTU. As a guide, 1 hp is about 9,000 BTU/h, 1.5 hp about 12,500 BTU/h and 2 hp about 18,000 BTU/h. The calculator maps your cooling load to the nearest standard hp class.
No. An oversized air-conditioner cools the air quickly but switches off before it removes enough humidity, leaving the room cold and clammy, and the frequent on/off cycling wastes energy and wears the compressor. Right-sizing — matching capacity to the load — gives the best comfort and efficiency.
A non-inverter compressor runs at full speed then switches off when the set temperature is reached, cycling on and off. An inverter varies the compressor speed to hold the temperature steadily, which avoids the energy spikes of restarting. In Singapore the two are no longer separated by their rating: since 1 April 2025 both must meet a coefficient of performance of at least 4.86, measured as COPweighted for inverters and at full load for fixed-speed units. That is why this calculator shows a single running cost for Singapore rather than a comparison — the two types are rated to the same number, and there is no published figure for how much a fixed-speed unit loses to cycling over a real month.
It converts the unit’s cooling capacity to the electrical power it draws using a coefficient of performance (COP), multiplies by your daily hours and 30 days to get kilowatt-hours, then applies your electricity tariff and grid carbon factor. For Singapore the COP used is 4.86, the minimum any single-split unit up to 17.6 kW may be sold at since 1 April 2025 — a floor rather than a typical value, so the result is an upper bound for a new unit and an older one will cost more. For markets where no minimum has been sourced it falls back to typical planning figures of 3.5 for an inverter and 2.8 for a non-inverter, which are estimates rather than regulated values. You can override the tariff with the rate from your bill, and in Singapore you can enter your own unit’s rated COP from its energy label.
The calculator will not answer that, and the reason is worth stating plainly. Both types now have to clear the same 4.86, so there is no difference in the rated numbers to price a premium against. The two are measured differently — an inverter on a part-load blend, a fixed-speed unit at full load — so an inverter is very likely still cheaper to run in practice, but nobody publishes how much a fixed-speed unit gives back to cycling over a mixed-load month, and inventing that figure would make the payback look precise when it is guesswork. Where no minimum standard has been sourced the tool still shows the comparison and a payback on typical figures. In Singapore, judge the two on the rated COP printed on each model’s energy label, along with noise, humidity control and warranty.
Yes. A room with large west-facing windows takes a heavy heat gain from the afternoon sun, so it needs more cooling capacity than a shaded room of the same size. The exposure setting applies a multiplier to the base load to account for this.
Around 24–25 °C is comfortable and efficient for most people in the tropics. Every degree lower increases energy use noticeably, so combining a moderate setpoint with a fan to move air is usually cheaper and just as comfortable as a very low thermostat.
They are good estimates for planning, not a guaranteed bill. Real performance depends on the specific model’s rating, insulation, outdoor temperature, how well the room is sealed, and maintenance. The efficiency default is a regulated minimum where one has been sourced and a typical planning figure otherwise, so neither is a measurement of your unit. The single biggest improvement you can make to the estimate is to read the coefficient of performance off your model’s energy label and type it into the efficiency field.
Completely free, with no account or usage limit. It runs entirely in your browser, collects no data, and works offline once the page has loaded.

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Method & sources

How it computes

Cooling load = floor area × ~600 BTU/h·m² (tropical baseline) × a sun-exposure factor, plus 600 BTU/h for each occupant beyond two, rounded up to the nearest standard hp class. Running cost converts that capacity to electrical draw as (BTU/h ÷ 3.412) ÷ COP, then × hours × 30 days ÷ 1000 for monthly kWh, × your tariff for cost and × the grid factor for CO₂. The COP is Singapore's regulated minimum of 4.86 where that applies, or your own unit's rated figure if you enter it.

What this tool implements

Singapore running costs use COP 4.86, the Minimum Energy Performance Standard for single-split units up to 17.6 kW since 1 April 2025. The one-year grace period for clearing existing stock ended on 31 March 2026, so the floor now binds on everything on sale.
⚠️ A FLOOR IS NOT A TYPICAL VALUE. 4.86 is the least efficient unit that may legally be sold, so the Singapore figure is an UPPER BOUND on what a new unit should cost to run. A unit bought before the standard changed will cost more, which is why the tool takes your own rated figure from the energy label.
The tool shows ONE running cost for Singapore rather than an inverter-versus-non-inverter comparison, because the floor applies to both types at the same number — 4.86 each. It is measured differently for each (COPweighted for inverters, COP at full load for fixed-speed), and no published source quantifies what a fixed-speed unit gives back to on/off cycling over a mixed-load month. Manufacturing that gap to keep a comparison alive would have made the payback figure look precise when it was a guess.
COPweighted is 0.4 × COP at 100% load + 0.6 × COP at 50%, so it already describes mixed duty — which is the right basis for a monthly bill, and is stated on the page rather than left implicit.
Markets with no sourced minimum standard keep the older side-by-side comparison on typical planning figures of COP 3.5 and 2.8, labelled as unsourced estimates rather than presented as regulated values.
⚠️ The model assumes the unit delivers its full rated capacity for every hour entered. A real unit modulates or cycles to match the actual load, so both figures are conservative.

Sources

National Environment Agency (Singapore). Circular NEA-LSD-CIRCULAR-ECA-00002-2025, 19 February 2025 — "Requirements for regulated goods under the Energy Conservation Act with effect from 1st April 2025", Annex B: revised MEPS for split-type air-conditioners, COPweighted ≥ 4.86 (inverter) and COP100% ≥ 4.86 (non-inverter) for single-split units up to 17.6 kW: https://www.nea.gov.sg/docs/default-source/cmd-documents/energy-e…)1-with-effect-from-1st-april-2025.pdf
Energy Market Authority of Singapore / SP Group — regulated domestic electricity tariff, 1 July to 30 September 2026, used for the default cost per kWh: https://www.ema.gov.sg/consumer-information/electricity/buying-el…
International Energy Agency — national grid carbon intensity factors (2022–2024), used for the kg CO₂ per kWh figure: https://www.iea.org/data-and-statistics

What can make this go out of date

⚠️ THE SINGAPORE TARIFF IS REVISED QUARTERLY and the shipped value is the 1 Jul–30 Sep 2026 rate. It is a default, not a measurement — the tariff field takes the figure from your own bill.
⚠️ THE MEPS FLOOR IS A REGULATORY VALUE THAT HAS ALREADY MOVED ONCE, from 4.04 to 4.86. Re-check it against the current NEA circular each review rather than treating 4.86 as permanent.

Air-Conditioner Sizing & Running Cost Calculator