Air conditioner size for Singapore rooms: rule and 7-day check

In Singapore, NEA’s rule of thumb for air conditioner size is: cooling capacity in kW = the floor area you air-condition, in m², ÷ 5. Multiply the kW by 3,412 for BTU/hr. For illustrative room sizes, our arithmetic gives 2.4 kW (about 8,189 BTU/hr) for a 12 m² bedroom and 4.0 kW (13,648 BTU/hr) for a 20 m² living room. NEA calls this a rule of thumb and sends readers to their supplier for a more detailed assessment.

Size matters both ways. According to NEA’s buying tips, an oversized unit costs more to run and may not dehumidify adequately, while an undersized one will not provide adequate cooling and dehumidification. This guide adds a room worksheet, a delivery-day label check and a seven-day log. The rule and the label come from NEA. The worksheet and the log are our own method, because NEA publishes no pass mark for how a well-sized unit should feel.

How many kW of air-con does my room need?

1. Measure the floor of the space the unit will cool, in metres: length × width. A 3 m × 4 m bedroom (an illustrative size) is 12 m². If your plan is in square feet, divide by 10.764 (a standard unit conversion, not from NEA; 129 sq ft is about 12 m²).
2. Divide by 5: 12 ÷ 5 = 2.4 kW.
3. For BTU/hr, multiply by 3,412: 2.4 × 3,412 = 8,188.8, so about 8,189 BTU/hr.
4. For an illustrative 4 m × 5 m living room: 20 ÷ 5 = 4.0 kW, and 4.0 × 3,412 = 13,648 BTU/hr.

An aircon BTU calculator is only this arithmetic. To go the other way, divide BTU/hr by 3,412 (our arithmetic, using NEA’s factor): a fictional 9,000 BTU/hr listing is about 2.64 kW (9,000 ÷ 3,412 = 2.638). The energy label’s Size line is in kW. NEA’s formula says “total aircon floor area”. For an open-plan space we read that as the part you intend to cool, so tell the supplier how you measured.

Which rooms need more than the rule gives?

NEA says a larger air-conditioner may be needed for rooms with double volume (double ceiling height), a large window area such as full-height glass windows, windows orientated towards the sun (east-west), or additional heat sources such as bar fridges. It states no percentage for any of these, so we do not add one. Mark each yes or no on the worksheet and treat any yes as a question for the supplier.

Why can an oversized air-con dehumidify badly?

NEA’s buying tips note that air-conditioners control both temperature and humidity. An oversized system, NEA says, “cools too quickly before moisture can be reduced”, so it may not dehumidify adequately and costs more to operate. An undersized one will not provide adequate cooling and dehumidification, so bigger is not the safe choice.

NEA does not say how far above the rule is too far, so the worksheet records one number of our own to ask about: label kW ÷ rule kW. For the illustrative 2.4 kW bedroom, take two fictional units, one labelled 2.64 kW and one labelled 3.52 kW. The ratios are 1.1 (2.64 ÷ 2.4) and 1.47 (3.52 ÷ 2.4). Neither is a pass or a fail. The ratio lets you ask: “My rule figure is 2.4 kW and this unit is 3.52 kW; what assessment makes it right?”

What if I am cooling two rooms with a multi-split?

NEA says a multi-split’s total cooling capacity is usually the sum of the individual rooms’ capacities, but a smaller total may be sufficient if the room units are not all turned on at the same time. It gives no figure. Our illustrative example: a 12 m² bedroom (2.4 kW) and a 9 m² study (9 ÷ 5 = 1.8 kW) sum to 4.2 kW, about 14,330 BTU/hr (4.2 × 3,412 = 14,330.4). If the bedroom runs at night and the study by day, ask the supplier what smaller total it proposes and on what assumption. Our own extra question, which NEA does not address: what can the system deliver to the bedroom when it is the only room running?

What should I check before I pay? A worksheet for each room

This worksheet is our own, not an NEA form. Only the area ÷ 5 rule, the four room flags and the label fields come from NEA.

• Room and when it is used:
• Length × width = floor area (m²):
• Rule figure: area ÷ 5 = kW, and kW × 3,412 = BTU/hr if the listing uses BTU:
• Flags, yes or no: double height; large windows; east or west sun; extra heat source:
• Unit considered: brand, model, label kW, ticks, kWh:
• Ratio: label kW ÷ rule kW (a question to ask, not a pass mark):
• Multi-split only: rooms that run together, and the supplier’s total and reason:
• Supplier’s size assessment: who gave it, when, in writing?
• Return or adjustment terms: read and saved with the date:

Does the unit that arrives match the listing?

NEA’s energy label page says an air-conditioner label shows, among other details, brand, model, type, size, ticks, annual energy consumption in kWh and registration number. For single-split and multi-split units, only the outdoor unit’s model number is displayed, and for split types the label is affixed to the outdoor unit only. Size is the full load cooling capacity in kW, to two decimal places. The registration number is unique to the registered model and comes from NEA’s Certificate of Registration (COR).

NEA also says retailers are only allowed to display models that have the label affixed. For split types, if only the indoor unit is on display, the labels for all possible outdoor units must be displayed prominently beside it. A floor model with no label, or an indoor unit with no outdoor-unit labels beside it, is worth a question. Online listings must show a legible label beside the image or description or, where that is not practical, state the tick rating and the COR registration number (or supplier code) prominently.

On delivery day:

1. Find the label on the outdoor unit. Our suggestion: ask the installer to let you read and photograph it before installation, while it is easy to reach.
2. Compare it with your listing, quotation and invoice: brand, outdoor unit model, size in kW, ticks, and the registration number if the listing gives one.
3. If anything differs, ask in writing straight away, with the photographs, which unit was ordered and which was delivered.
4. NEA’s consumer advisory says to purchase only NEA-registered appliances found in its Database of Registered Goods, and asks the public to report regulated goods with no label, or not registered, to NEA_energylabel@nea.gov.sg. We could not open the database when this guide was researched on 3 October 2026 and did not retry it on 17 October, so we do not describe how to search it.

What does a seven-day fit log look like?

Keep the conditions steady:

• Set 25°C every day. NEA’s energy-saving tips suggest it and say that the lower the setting, the more energy the air-conditioner uses. Our suggestion: write down any day you lower it, because that can hide a poor fit.
• Close curtains or blinds during the hottest part of the day, as NEA suggests, and do the same each day.

Each day, write down the hours run, the weather, who was in the room, which other heat sources were on, how long the room took to feel comfortable and how the air felt: dry, fine or clammy. A hygrometer reading at the same time daily can help, though NEA gives no target. Vary the conditions:

1. Delivery day: label check, then a first evening run. Note how long until the room is comfortable.
2. A sunny afternoon when the sun reaches the windows, blinds closed.
3. A full night. Note how the room feels on waking.
4. A day with more people home or extra heat sources on, plus a humid or rainy spell if one comes.
5. NEA’s timer tip: set the timer to switch off half an hour earlier than usual and note how long the room stays comfortable.
6. Day 7: read the log and decide.

What should the log make me do?

These readings are ours, mapped to NEA’s two warnings:

• Not comfortable at 25°C on several days despite long runs, especially in afternoon sun: this matches NEA’s description of an undersized unit, or a room with one of the flags. Ask the supplier for the detailed assessment NEA recommends.
• The room reaches 25°C quickly but the air stays damp or sticky: this matches NEA’s description of an oversized unit. Compare the label kW with your worksheet and ask why that size.
• Comfortable and not clammy: no sign of a mismatch. Keep the log beside your first electricity bills.

A log cannot separate size from installation, airflow or weather, so treat a pattern as a question for the installer. NEA also says to check the air filter once a month and have the unit serviced regularly and inspected annually. On day 7, send the worksheet, label photograph and log to the supplier in writing and ask for their size assessment and its basis. Whether an installed unit can be returned as the wrong size may depend on the seller’s written terms (general information, not legal advice); our home-trial guide explains how to read them. If the unit seems faulty rather than badly matched, see our faulty-purchase guide.

Is there a best air conditioner for a Singapore room?

The NEA pages we read do not rank brands or models. For questions to put to a seller about “energy-saving” or “best in class” claims, see eco-friendly claims. Our suggested order of questions: size the room, check the unit is labelled and registered, then compare kWh between models of similar capacity. Our energy label guide shows how to rescale a label’s kWh to your own hours and electricity rate, and why a larger unit can carry more ticks and still use more electricity. The appliance running cost calculator does that arithmetic from a label’s kWh, or from watts and hours, and compares two units with a payback on the price gap; it is arithmetic on figures you enter, not a rule.

NEA’s minimum standards page sets minimum coefficients of performance for casement and window, split and portable air-conditioners, plus standby power limits for split types; our minimum standards guide covers the tick floors. If you plan to use Climate Vouchers, size first, then check eligibility in our Climate Vouchers shortlist. If the new unit replaces an old one, ask when you order what happens to the old unit; our trade-in and recycling guide covers what NEA lists for retailer take-back. Another appliance sized from the room’s dimensions is an air purifier: see choosing one by CADR and room size. More guides are under Trying things out. This guide covers size and fit only, not installation rules or installers.

Common questions