About

Calculating the volume of a room is the first step in sizing heating, ventilation, and air conditioning (HVAC) systems. While a simple bedroom is a basic rectangular prism, real-world architecture often involves "L-shaped" living areas, alcoves, or open-plan spaces that defy a single length x width calculation. Accurate volume data is critical for determining British Thermal Unit (BTU) requirements for cooling and calculating Air Changes Per Hour (ACH) for air purifiers or industrial ventilation.

This tool adopts a "Zone Summation" approach. Users can break a complex room into simple rectangular subsections (zones). The tool sums these zones to provide the total cubic footage and cubic meters. It also provides a baseline estimate for cooling power required based on volume, though insulation and window direction also play key roles.

Formulas

The total volume is the sum of all defined rectangular zones:

V_total = n∑i=1 (L_i × W_i × H_i)

Cooling Estimation (Rule of Thumb):

BTU ≈ Volume_ft³ × 4

Air Changes Per Hour (ACH):

ACH = CFM × 60Volume_ft³

Reference Data

Space Type	Target ACH (Air Changes/Hour)	Est. Cooling (BTU/sq ft approx)	Notes
Residential Bedroom	5 - 6	20	Standard ceiling height (8ft).
Residential Kitchen	15 - 20	35	Heat generation from appliances requires higher ACH.
Bathroom	10 - 15	N/A	Ventilation is priority over cooling.
Office (Open Plan)	4 - 6	25	Account for computer heat load.
Server Room	20 - 30+	> 100	Critical cooling. Volume calculation essential for fire suppression gas (FM-200).
Garage	4 - 6	Variable	Exhaust ventilation focus.

Frequently Asked Questions

Formulas like Length x Width only work for perfect rectangles. If your room is L-shaped, T-shaped, or has a bay window, treating it as one big rectangle will overestimate the volume. Breaking it into smaller "boxes" and adding them together yields 100% accuracy.

Significantly. Most HVAC rules of thumb are based on square footage assuming 8-foot ceilings. If you have 12-foot cathedral ceilings, you have 50% more air volume to treat. Using a calculator based on volume (cubic ft) rather than area (sq ft) prevents undersizing your unit.

CFM stands for Cubic Feet per Minute. It is the standard rating for fans, air purifiers, and AC blowers. By inputting the CFM of your device, this tool calculates how many times per hour that device can filter/replace all the air in the calculated volume.

Yes. Select "Meters" in the tool. The calculation will output Cubic Meters. Note that the BTU estimate is primarily an Imperial standard, so it converts the metric volume to feet internally to give you the BTU rating, but displays volume in your chosen unit.