Cooling · BTU/h
BTU Calculator
A 12 × 15 ft room with an 8 ft ceiling needs roughly 20,400 BTU/h of cooling in a hot climate — about 1.7 tons, or a 1.5 HP split. Enter your room below for the exact figure in BTU/h, tons, kilowatts and horsepower.
Room dimensions
- Tons
- 2.45 t
- Kilowatts
- 8.64 kW
- Horsepower
- 3.68 HP
- Room area
- 19.32 m²
- Room volume
- 58.9 m³
Cooling capacity
29,450BTU/h
≈ 2.45 tons · 8.64 kW
What size air conditioner do I need?
Take the result above and round up to the nearest capacity actually sold. These are the sizes on the shelf.
| Unit size | Typically fits | Type |
|---|---|---|
| 5,000 BTU | Small bedroom, home office (shaded) | Window |
| 8,000 BTU | Standard bedroom | Window / portable |
| 10,000 BTU | Large bedroom, small living room | Window / portable |
| 12,000 BTU | Living room, studio apartment | Mini-split / window |
| 18,000 BTU | Large living room, open-plan area | Mini-split |
| 24,000 BTU | Very large room, small open floor | Mini-split |
| 36,000 BTU | Open floor plan, small shop | Mini-split / ducted |
BTU chart by room size
For a single room, at 8 ft ceilings. The ENERGY STAR column is the published room-unit recommendation for a temperate climate; the hot-climate column is this site's volumetric method. Treat them as the floor and the ceiling of a sensible range.
| Room | m² | ENERGY STAR | Hot climate | Tons (hot) |
|---|---|---|---|---|
| 100 sq ft | 9 | 5,000 | 11,334 | 0.9 |
| 150 sq ft | 14 | 5,000 | 17,001 | 1.4 |
| 200 sq ft | 19 | 6,000 | 22,668 | 1.9 |
| 250 sq ft | 23 | 6,000 | 28,335 | 2.4 |
| 300 sq ft | 28 | 7,000 | 34,003 | 2.8 |
| 350 sq ft | 33 | 8,000 | 39,670 | 3.3 |
| 400 sq ft | 37 | 9,000 | 45,337 | 3.8 |
| 450 sq ft | 42 | 10,000 | 51,004 | 4.3 |
| 500 sq ft | 46 | 12,000 | 56,671 | 4.7 |
| 600 sq ft | 56 | 14,000 | 68,005 | 5.7 |
| 700 sq ft | 65 | 14,000 | 79,339 | 6.6 |
| 800 sq ft | 74 | 18,000 | 90,673 | 7.6 |
| 1,000 sq ft | 93 | 18,000 | 113,342 | 9.4 |
ENERGY STAR adjustments: add 10% for a very sunny room, subtract 10% for a heavily shaded one, add 600 BTU/h per occupant beyond two, and add 4,000 BTU/h for a kitchen.
Whole-home sizing
Above roughly 1,000 sq ft the question stops being about a room unit and becomes a central system, sized on BTU per square foot by climate. Per-room formulas scaled up overstate this badly: interior rooms carry almost no envelope load, and rooms do not all peak at once.
| House | Mild · 20/sq ft | Moderate · 25 | Hot · 30 | Tons |
|---|---|---|---|---|
| 1,000 sq ft | 20,000 | 25,000 | 30,000 | 1.7–2.5 |
| 1,200 sq ft | 24,000 | 30,000 | 36,000 | 2–3 |
| 1,500 sq ft | 30,000 | 37,500 | 45,000 | 2.5–3.8 |
| 1,800 sq ft | 36,000 | 45,000 | 54,000 | 3–4.5 |
| 2,000 sq ft | 40,000 | 50,000 | 60,000 | 3.3–5 |
| 2,500 sq ft | 50,000 | 62,500 | 75,000 | 4.2–6.3 |
| 3,000 sq ft | 60,000 | 75,000 | 90,000 | 5–7.5 |
Above about 5 tons, residential equipment usually gives way to two systems or a zoned setup. For anything you will buy equipment from, get a Manual J — or work it out room by room with the HVAC load calculator.
AC tonnage: tons, BTU/h and kW
1 ton = 12,000 BTU/h. Room coverage assumes a shaded room with a 2.7 m ceiling in a hot climate.
| Tons | BTU/h | kW | Covers about |
|---|---|---|---|
| 0.75 | 9,000 | 2.64 | 7 m² / 72 sq ft |
| 1 | 12,000 | 3.52 | 9 m² / 96 sq ft |
| 1.5 | 18,000 | 5.28 | 13 m² / 144 sq ft |
| 2 | 24,000 | 7.04 | 18 m² / 191 sq ft |
| 2.5 | 30,000 | 8.8 | 22 m² / 239 sq ft |
| 3 | 36,000 | 10.56 | 27 m² / 287 sq ft |
| 4 | 48,000 | 14.08 | 36 m² / 383 sq ft |
| 5 | 60,000 | 17.6 | 44 m² / 478 sq ft |
Aircon size in HP
Where aircons are sold by horsepower — the Philippines, Malaysia, much of Southeast Asia — 1 HP is about 9,000 BTU/h, and rooms are measured in square metres. Plan 600–800 BTU per square metre in a tropical climate.
| HP | BTU/h | Room (m²) |
|---|---|---|
| 0.5 | 5,000 | up to 7 |
| 0.75 | 7,000 | 7–10 |
| 1.0 | 9,000 | 10–14 |
| 1.5 | 12,000 | 14–18 |
| 2.0 | 18,000 | 18–26 |
| 2.5 | 24,000 | 26–34 |
| 3.0 | 30,000 | 34–42 |
HP on an aircon labels cooling capacity, not motor power: a 1 HP unit delivers around 2.6 kW of cooling while drawing roughly 0.8–1 kW of electricity, and less than that on an inverter once the room is cool.
BTU by room dimensions
Computed with the same formula as the calculator above (hot-climate volumetric method).
| Room | Area | BTU/h (shaded) | BTU/h (sunny) | Tons |
|---|---|---|---|---|
| 10 × 10 ft (8 ft ceiling) | 100 sq ft | 11,327 | 13,592 | 0.9 |
| 12 × 12 ft (8 ft ceiling) | 144 sq ft | 16,311 | 19,573 | 1.4 |
| 12 × 15 ft (8 ft ceiling) | 180 sq ft | 20,388 | 24,466 | 1.7 |
| 15 × 20 ft (8 ft ceiling) | 300 sq ft | 33,980 | 40,776 | 2.8 |
| 20 × 20 ft (9 ft ceiling) | 400 sq ft | 50,970 | 61,164 | 4.2 |
| 25 × 20 ft (9 ft ceiling) | 500 sq ft | 63,713 | 76,455 | 5.3 |
| 30 × 25 ft (9 ft ceiling) | 750 sq ft | 95,569 | 114,683 | 8 |
The formula
BTU/h = length(m) × width(m) × height(m) × factor
factor = 500 (shaded room)
factor = 600 (sun-exposed room)
tons = BTU/h ÷ 12,000
kW = tons × 3.52
HP = BTU/h ÷ 8,000Example: a 4 × 5 m room with 3 m ceilings, shaded — 60 m³ × 500 = 30,000 BTU/h, which is 2.5 tons or 8.8 kW. Sizing several rooms at once? Use the room-by-room load calculator; picking a specific unit, the mini split sizing guide.
FAQ
- What size air conditioner do I need for my room?
- Multiply the room's volume in cubic metres by 500 BTU/h, or by 600 if it takes direct sun, then round up to the nearest unit sold. A 12 × 15 ft room with an 8 ft ceiling comes to about 20,000 BTU/h on that hot-climate method; the ENERGY STAR chart puts the same 180 sq ft room at 6,000 BTU/h for a temperate climate. The gap is climate and construction, not a mistake — pick the column that matches where you live.
- How is this BTU number calculated?
- BTU/h = length × width × height (in metres) × 500, or × 600 when the room gets direct sun. Because it works from volume rather than floor area, a high ceiling correctly raises the result. Tons are BTU/h divided by 12,000, kilowatts are tons × 3.52, and HP is BTU/h divided by 8,000.
- How many BTU per square foot?
- In mild climates plan 20–25 BTU per square foot at 8-foot ceilings. The volumetric method used by this calculator works out near 110 BTU per square foot, which is a hot-climate figure. Both are in the charts below, in separate columns, because averaging them would describe nowhere.
- What is a ton of air conditioning?
- One ton of refrigeration equals 12,000 BTU/h — historically the cooling delivered by melting a ton of ice in 24 hours. So 1.5 tons is 18,000 BTU/h and 2 tons is 24,000 BTU/h. It measures capacity, not the weight of the equipment.
- How many HP is 1 aircon?
- In the Philippines, Malaysia and much of Southeast Asia, 1 HP of aircon is about 9,000 BTU/h. The ladder runs 0.5 HP (5,000 BTU), 0.75 HP (7,000), 1.0 HP (9,000), 1.5 HP (12,000), 2.0 HP (18,000) and 2.5 HP (24,000). HP here labels cooling capacity, not motor power or the electricity drawn.
- Should I round up or down to the nearest unit size?
- Round up when the room gets direct sun, holds several people or appliances, or sits in a hot climate. Round down only when it is shaded, well insulated and in a mild climate — and never by more than one step in either direction.
- What happens if the AC is too big?
- An oversized unit cools the air quickly and shuts off before it has removed the humidity, which leaves the room cold and clammy. It also cycles on and off more often, adding wear and energy use. Too small is the opposite failure: it runs continuously without ever reaching the set temperature.
- Does ceiling height matter?
- Yes, and it is where per-square-foot rules break down. This calculator works from volume, so a 12 ft ceiling raises the result by 50% against an 8 ft one. The square-foot charts on this page assume 8 ft and need scaling up if yours is higher.
- Is this a Manual J load calculation?
- No. This is a fast field estimate. A full ACCA Manual J models insulation R-values, window area and orientation, infiltration and local design temperatures. Use this page to land in the right range and sanity-check a quote; use a Manual J for permits and final equipment selection.