Calculate the recommended cooling capacity (BTU/hr) for your room.
Low (Shaded, minimal windows)
Medium (Some direct sun or average windows)
High (Large windows, direct afternoon sun)
Enter room dimensions to see your recommended BTU/hr.
Understanding Air Conditioner Cooling Capacity (BTU/hr) and Room Size
Choosing the right air conditioner for your space is crucial for comfort and energy efficiency. The primary metric for an air conditioner's cooling power is its BTU/hr (British Thermal Units per hour). This value indicates how much heat the unit can remove from a room in one hour. Using an air conditioner with insufficient BTU/hr will result in inadequate cooling, while an oversized unit can lead to frequent on-off cycles, poor dehumidification, and wasted energy.
This calculator helps you estimate the ideal cooling capacity needed based on your room's size and other factors. The calculation uses a standard formula that considers the room's volume and then adjusts for external and internal heat loads.
The Calculation Formula
The basic principle is to calculate the room's volume and then apply a baseline BTU/hr per cubic meter. We then adjust this based on several factors:
Room Volume: Calculated as Length × Width × Height. Larger volumes require more cooling.
Baseline BTU/hr per Cubic Meter: A general guideline is around 50 BTU/hr per cubic meter. This is a starting point.
Sun Exposure Factor: Rooms that receive direct sunlight (especially afternoon sun) or have large windows will heat up more. A multiplier (e.g., 1.0 for low, 1.1 for medium, 1.25 for high) is applied.
Occupancy Factor: Each person generates heat. We add a certain amount of BTU/hr per person beyond the first two. A common estimate is 600 BTU/hr per additional person.
Heat Generating Items: Appliances like televisions, computers, and gaming consoles also generate heat. We add an estimated BTU/hr for these items. A common estimate is 1000 BTU/hr per significant item.
*Note: The exact base BTU/m³ and per-occupant/item values can vary slightly based on regional standards and specific conditions, but this calculator uses commonly accepted approximations.*
Factors Affecting Your Choice
Room Dimensions: The most significant factor. Ensure you measure accurately in meters.
Ceiling Height: Higher ceilings mean a larger volume of air to cool.
Sunlight: Rooms facing west or south, or those with large, unshaded windows, will require a more powerful unit.
Insulation: Poorly insulated rooms or those with drafty windows may need a higher BTU rating.
Occupancy: Consider how many people typically use the room.
Electronics: Count any significant heat-producing electronics.
Purpose of the Room: A kitchen might need more cooling than a bedroom due to heat from appliances.
How to Use the Calculator
1. Enter the Length, Width, and Height of your room in meters.
2. Select the level of Sun Exposure for the room.
3. Enter the typical number of Occupants. The calculator automatically accounts for additional occupants beyond the first two.
4. Estimate the number of significant Heat Generating Items (like TVs, computers, game consoles).
5. Click the "Calculate Required BTU/hr" button.
The result will provide a recommended BTU/hr capacity for your air conditioner. It's generally advised to choose an air conditioner with a BTU rating close to, or slightly above, the recommended value. If your calculation falls between standard AC sizes, it's often better to round up slightly.
function calculateCoolingCapacity() {
var length = parseFloat(document.getElementById("roomLength").value);
var width = parseFloat(document.getElementById("roomWidth").value);
var height = parseFloat(document.getElementById("roomHeight").value);
var sunExposure = parseFloat(document.getElementById("sunExposure").value);
var occupancy = parseInt(document.getElementById("occupancy").value);
var heatItems = parseInt(document.getElementById("heatGeneratingItems").value);
var resultDiv = document.getElementById("result");
// Clear previous results and error messages
resultDiv.innerHTML = ";
// Input validation
if (isNaN(length) || length <= 0 ||
isNaN(width) || width <= 0 ||
isNaN(height) || height <= 0 ||
isNaN(occupancy) || occupancy < 1 ||
isNaN(heatItems) || heatItems < 0) {
resultDiv.innerHTML = 'Please enter valid positive numbers for all dimensions and occupancy.';
return;
}
var baseBTUPerCubicMeter = 50; // Standard baseline
var btuPerAdditionalOccupant = 600;
var btuPerHeatItem = 1000;
var roomVolume = length * width * height;
var baseCoolingNeeds = roomVolume * baseBTUPerCubicMeter;
var occupancyAdjustment = 0;
if (occupancy > 2) {
occupancyAdjustment = (occupancy – 2) * btuPerAdditionalOccupant;
}
var heatItemAdjustment = heatItems * btuPerHeatItem;
var totalBTU = (baseCoolingNeeds * sunExposure) + occupancyAdjustment + heatItemAdjustment;
// Round to the nearest hundred for practical AC unit sizes
var roundedBTU = Math.round(totalBTU / 100) * 100;
// Ensure a minimum reasonable BTU for very small spaces
if (roundedBTU < 5000) {
roundedBTU = 5000;
}
resultDiv.innerHTML = 'Recommended Cooling Capacity: ' + roundedBTU.toLocaleString() + ' BTU/hr';
}