The physical relationship
The calculator starts with area × height × a base load per cubic metre, then multiplies by the selected solar exposure. It adds a heat allowance for people beyond the first occupant and for appliances that release heat into the room. The result is cooling capacity, not electricity consumption.
A checked case
For a 20 m² room with a 2.6 m ceiling, volume is 52 m³. At 40 W/m³ the base is 2,080 W. Strong afternoon sun at a 1.20 factor raises it to 2,496 W. Two extra occupants add 240 W and a computer adds 180 W, producing a 2,916 W estimate, commonly described as about 2.9 kW of cooling.
Useful planning use
Use it to shortlist a room unit, compare a shaded bedroom with a glazed office, or see why a unit that was adequate in spring struggles during a sunny afternoon.
Failure modes in this measurement
Treating floor area alone as the whole heat load is the usual mistake. A high ceiling, open stairwell, west-facing glass, cooking, servers, and unsealed doors all change the load. Do not confuse a unit's cooling kW with the kW shown on an electricity meter; efficiency links them but they are not the same measurement. Oversizing can also leave short cycles and poor humidity removal.
What makes this quantity different
This calculator sizes a cooling output from estimated heat entering one room. The appliance-energy page estimates billed electricity from a known electrical wattage and running time. Neither page selects refrigerant pipework, a breaker, ventilation, or a model for a whole-house duct system.
Field check before acting
Run a conservative and a hot-day scenario. Record whether doors stay closed, whether sun is blocked outside, and which heat-producing equipment runs at the same time. An undersized portable unit may also reject heat through a hose that leaks replacement air into the room, a loss the simple room model cannot see.
Limits of the model
Final equipment selection needs the manufacturer's rated conditions and, for difficult rooms, a competent installer’s load assessment. The browser keeps the dimensions local; it cannot inspect insulation gaps, condensation risk, or electrical suitability.