# Air Conditioner BTU Calculator

URL: https://speedycalculator.com/calculators/construction/ac-btu/
Last updated: 2026-10-25

> The air conditioner BTU calculator sizes a room air conditioner from the Energy Star room-area chart, adjusted for ceiling height, sun exposure, extra occupants and kitchens, in BTU/h, tons and kW.

## Inputs

- Room area (ft², m², yd², acre)
- Ceiling height (ft, m, in, yd, cm)
- Sun exposure
- Regular occupants
- Room includes a kitchen

## Results

- Base capacity (Energy Star chart)
- Recommended capacity
- Tons

## Formula

```
Base capacity from the Energy Star chart (5,000 BTU/h for 100–150 ft² … 34,000 for 2,000–2,500 ft²)
× ceiling height ÷ 8 ft, × 1.10 sunny or 0.90 shaded
+ 600 BTU/h per person beyond two, + 4,000 BTU/h for a kitchen
```

## Explanation

Window and portable air conditioners are rated in BTU per hour. Energy Star publishes a simple chart that matches capacity to room area for a typical 8 ft ceiling, then suggests a few adjustments: about 10% more for very sunny rooms, 10% less for shaded rooms, 600 BTU/h for each regular occupant beyond two and 4,000 BTU/h if the unit cools a kitchen.

### How to use the Air Conditioner BTU Calculator

- **Room area**
- **Ceiling height**
- **Sun exposure**
- **Regular occupants**
- **Room includes a kitchen**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the room area, ceiling height, sun exposure, the number of people who usually use the room and whether it includes a kitchen. The calculator looks up the base capacity and applies each adjustment.

### Energy Star sizing chart

Area (ft²)BTU/h100–1505,000150–2506,000250–3007,000300–3508,000350–4009,000400–45010,000450–55012,000550–70014,000700–100018,0001000–120021,0001200–140023,0001400–150024,0001500–200030,0002000–250034,000

### Tips for an accurate estimate

- Take measurements at floor level and at the ceiling – walls and rooms are often slightly out of square.
- Use the manufacturer's coverage, spacing and installation data when it differs from the typical values here.
- Keep a little extra of every finish material for touch-ups and repairs later.
- Check local building codes and permits before structural, electrical, plumbing or gas work.

### Common mistakes to avoid

- Sizing heating or cooling equipment by area alone when insulation, windows and climate make a big difference.
- Buying too little paint, stain or flooring and ending up with mismatched batches.
- Overlooking the extra material for steps, railings, gables and trim.

### Inputs explained

FieldWhat to enterRoom areaUnits: ft², m², yd², acreCeiling heightUnits: ft, m, in, yd, cmSun exposureChoose one: Normal, Very sunny (+10%), Heavily shaded (−10%)Regular occupantsA numberRoom includes a kitchenChoose one: No, Yes

### What each result means

- **Recommended capacity** = ([Base capacity (Energy Star chart)]×[Ceiling height]÷2.4384×[Sun exposure] + 600×max([Regular occupants] - 2, 0) + 4000×[Room includes a kitchen])
- **Tons** = [Recommended capacity]÷12000

## Worked example

Inputs — Room area: 350 ft²; Ceiling height: 8 ft; Sun exposure: Normal; Regular occupants: 2; Room includes a kitchen: No.

Results — Base capacity (Energy Star chart) = 8,000 BTU/h; **Recommended capacity = 8,000 BTU/h**; Tons = 0.67.

## FAQ

**What size air conditioner for a 350 ft² room?**
8,000 BTU/h by the Energy Star chart, more for a sunny room or high ceiling.

**How many square feet does 12,000 BTU cool?**
About 450–550 ft² in typical conditions.

**Should I round up?**
Choose the nearest standard size; avoid going much bigger, which leaves the room cold and damp.

**What formula does the Air Conditioner BTU Calculator use?**
Base capacity from the Energy Star chart (5,000 BTU/h for 100–150 ft² … 34,000 for 2,000–2,500 ft²).


## Sources

- [Energy Star – Room air conditioner sizing](https://www.energystar.gov/products/room_air_conditioners)