Construction & Home

Air Conditioner Size Calculator

Estimates the cooling capacity in BTU per hour and refrigeration tons needed for a room from its floor area in square feet, at about 20 BTU per square foot.

What this calculator does

The Air Conditioner Size Calculator estimates your result instantly from the values you enter, using standard construction & home formulas. Estimates the cooling capacity in BTU per hour and refrigeration tons needed for a room from its floor area in square feet, at about 20 BTU per square foot. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.

Air Conditioner Size Calculator

Result

—
Cooling Capacity (BTU/hr)
—
Tons

About Air Conditioner Size Calculator

Choosing an air conditioner? Enter your room’s floor area in square feet and this calculator estimates the cooling capacity you need, rounded to the nearest 100 BTU per hour.

It applies a rule of about 20 BTU per square foot and converts the result into refrigeration tons, where one ton equals 12,000 BTU per hour.

Formula & Mathematical Calculation

Cooling Capacity (BTU/hr) = f(Room Area (ft²))

Calculated according to standard construction formulas implemented in the calculator core.

Calculation Example

For a 400 ft² room: BTU = round(400 × 20 ÷ 100) × 100 = round(80) × 100 = 8,000 BTU/hr.

Tons = 8,000 ÷ 12,000 = 0.67 tons. The calculator shows 8,000 BTU and 0.67 tons.

Key Benefits

  • Sizes cooling capacity from a single input, the room's floor area.
  • Applies roughly 20 BTU per square foot and rounds to the nearest 100 BTU.
  • Converts the BTU figure into refrigeration tons at 12,000 BTU per ton.
  • Gives a quick starting point before adjusting for sun, ceiling height, and occupancy.

How to Use this Calculator

  1. Enter the room area
    Type the room's floor area in square feet into the Room Area field.
  2. Calculate
    Select Calculate to size the unit.
  3. Read the results
    Read the Cooling Capacity in BTU per hour and the equivalent Tons in the result boxes.

Assumptions & Limitations

What the calculation assumes

  • Every value you enter is treated as an exact, known amount.
  • Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
  • Results use standard published formulas and account only for the values entered above.
  • Rounding is applied for display; the underlying calculation uses your full precision.
  • Results are returned in the same units you enter, unless the tool states the output unit.

What it does not cover

  • Air Conditioner Size Calculator produces a calculated result for reference and learning, not a certified or official measurement.
  • Real-world outcomes differ when tolerances, rounding rules or local standards apply.
  • Definitions and standards vary by region and change over time; verify the convention that applies to your case.
  • Figures are only as accurate as the inputs you supply — check them before acting on the result.
  • For work where the result carries real consequences, confirm it against an authoritative source.

Frequently Asked Questions

About 20 BTU per hour per square foot. The area is multiplied by 20, then rounded to the nearest 100 BTU.

The BTU-per-hour figure is divided by 12,000, since one ton of cooling equals 12,000 BTU per hour.

No. It is a floor-area rule of thumb and does not account for insulation, windows, climate, or ceiling height, which a detailed load calculation would include.

The estimate is rounded to the nearest 100 BTU per hour to match how cooling capacities are commonly quoted.

Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.