PROJECTMETER
Calculators/AC BTU

Room AC BTU Calculator

Size a room air conditioner from floor area, sunlight, regular occupants and kitchen use.

Free · No signup · Reviewed August 22, 2026
Step 1
Set your project size

Use the finished area you plan to cover, then refine the assumptions below.

Step 2 · Visual referenceCheck the active area
Living room with window air conditioner
Cooling load6,000 BTU/h target
  1. Base room capacity6,000 BTU/h

6,000 BTU/h is the room AC target after the active adjustments. This is a sizing guide, not a whole-home load calculation.

Floor area180 ft²Sun adjustmentNo changePeople + kitchenNo change

Why it mattersSee how sunlight, occupants and kitchen use change the cooling load.

Reference image; figures update from your measurements.

You’ll need

6000 BTU/h cooling capacity
Shopping list
6000adjusted BTU/h target
6000BTU/h area-table base
180sq ft cooled area
1 room$399.00 primary material estimate

Room AC sizing summary

Use the capacity target to compare correctly sized room air conditioners, then confirm installation, electrical and window requirements.

EquipmentAC BTUPackageroom air conditionerBasisENERGY STAR

How the calculation works

ENERGY STAR area capacity × sunlight adjustment + people + kitchen

The measured floor area selects an ENERGY STAR base capacity. Published sunlight, occupancy and kitchen adjustments are then applied without extrapolating beyond the table.

MEASURE WITH CONFIDENCE

How to use the ac btu calculator

Measure the floor length and width of the enclosed room, then select the real sunlight condition, regular occupancy and kitchen use. ProjectMeter follows the ENERGY STAR room-air-conditioner capacity table and applies its published adjustments to estimate cooling capacity in BTU per hour.

Formula and guidance reviewed August 22, 2026. Always confirm the final order with product instructions and project requirements.
STEP BY STEP

What to measure

  1. 01

    Measure the cooled floor area

    Record the longest finished room length and width at right angles. Split L-shaped or connected spaces into simple rectangles and add them as separate room entries only when one room air conditioner is genuinely expected to cool the combined open area.

  2. 02

    Classify sunlight honestly

    Choose heavily shaded only when the room receives limited direct solar gain, and very sunny when strong direct sun is a regular condition. ENERGY STAR recommends reducing capacity 10% for heavy shade or increasing it 10% for a very sunny room.

  3. 03

    Count regular occupants

    Enter the number of people who regularly use the room at the same time. The published adjustment starts above two occupants and adds 600 BTU per hour for each additional person; occasional visitors do not need to be treated as permanent load.

  4. 04

    Identify kitchen use and limits

    Turn on the kitchen adjustment only when the room air conditioner serves a cooking space; ENERGY STAR adds 4,000 BTU per hour. Rooms above the published 2,500 sq ft chart, high ceilings and unusual heat loads need a professional cooling-load calculation.

WORKED EXAMPLE

15 × 12 ft sunny room for three people

  • 180 sq ft enclosed floor area
  • 6,000 BTU/h ENERGY STAR base capacity
  • Very sunny: add 10%
  • Three regular occupants: add 600 BTU/h
Calculated result

The sunlight adjustment raises the base to 6,600 BTU/h, then the third regular occupant adds 600 BTU/h. The planning target is 7,200 BTU/h; compare nearby certified product capacities without assuming that a much larger unit is better.

Try your own measurements ↑
AVOID COSTLY REWORK

Common mistakes before you buy

  • Avoid deliberate oversizing. ENERGY STAR warns that an oversized room unit can cool too quickly to remove humidity effectively, leaving the space cool but damp.
  • Confirm the product's rated cooling capacity, mounting type, electrical requirements, window opening dimensions, support instructions and airflow direction before purchasing.
  • Use a qualified HVAC professional for whole-home systems, open multi-room layouts, unusually high ceilings, major west-facing glass, server or appliance heat, poor insulation or spaces beyond the chart.
FROM QUANTITY TO BUDGET

Compare the complete project cost

Your material quantity is only one part of a quote. Preparation, removal, access, finishing and local labour can change the installed total.

Replace an HVAC system$5,000–$22,000Compare HVAC replacement scopes by load, equipment efficiency, ductwork, electrical work, controls and permits.Read cost guide →Install a ductless mini-split$2,000–$5,000Compare ductless mini-split costs by verified load, zones, capacity, mounting, line routing, electrical work and commissioning.Read cost guide →
MEASURE BEFORE YOU ORDER

Planning guides for this calculator

Use the live model for feedback, then use these guides to verify the dimensions and material assumptions behind the result.

Measure & estimateRoom AC Sizing FactorsMeasure the room area and apply sunlight, occupancy and kitchen adjustments without treating BTU as a simple bigger-is-better number.Read guide →Choose & planWhy Oversized Air Conditioners Perform PoorlyUnderstand short cycling, humidity control and comfort before buying a room AC with more BTU than the sizing guidance.Read guide →Compare materialsWindow vs Portable vs Through-Wall Air ConditionerCompare room AC formats by rated capacity, exhaust, condensate, noise, security, window loss and installation constraints.Read guide →Specify & buyFixed-Speed vs Inverter Room Air ConditionerCompare compressor control, part-load comfort, noise, efficiency and price after choosing the correct room capacity.Read guide →Plan a projectBedroom Window AC PlanningSize and place a bedroom window air conditioner while checking window fit, circuit, drainage, noise and sleeping airflow.Read guide →Avoid failuresHow to Prevent Room AC Short Cycling and High HumidityReduce rapid compressor cycling and clammy comfort by sizing correctly, preserving airflow and managing moisture sources.Read guide →Time the workWhen and How to Install a Window Air ConditionerPrepare the opening, electrical supply, drainage and safe support before hot weather.Read guide →Protect & maintainWindow AC Seasonal Removal and StorageRemove, clean, dry and store a room AC without trapping water or damaging fins.Read guide →Manage the projectRoom air conditioning: Budget, Quotes, Safety and CloseoutManage a complete room air conditioning project from measured quantity and comparable bids through safety checks, maintenance records and final acceptance.Read guide →Worked exampleBTU for a 12 × 12 RoomSize an ordinary 144 sq ft room from the ENERGY STAR table and show how strong sun changes the target.Read guide →Worked exampleBTU for a 15 × 20 RoomCalculate a 300 sq ft room with strong sun and one regular occupant above the first two people.Read guide →Worked exampleBTU for a 400 Sq Ft KitchenApply the published kitchen adjustment to a 400 sq ft room AC sizing example.Read guide →
TAKE THE PLAN TO THE SITE

Interactive project checklists

Use the pre-order list before material arrives, then save the inspection and maintenance list for closeout and future care.

ROOM AIR CONDITIONER · READYRoom AC Purchase and Installation ChecklistVerify capacity, window, electrical supply, drainage, noise and secure mounting before buying.Open 12-task checklist →ROOM AIR CONDITIONER · CARERoom AC Seasonal Maintenance ChecklistInspect filters, airflow, mounting, drainage and operating behavior before and during cooling season.Open 12-task checklist →
COMMON QUESTIONS

AC BTU calculator FAQ

How many BTUs do I need for a 200 sq ft room?

The ENERGY STAR table places an area above 150 and up to 250 sq ft at a 6,000 BTU/h base capacity. Sunlight, regular occupants and kitchen use can change that planning target.

Is a larger room air conditioner always better?

No. An oversized unit may reach the thermostat setting before removing enough humidity, causing short cycling, lower efficiency and a clammy room. Match capacity to the measured space and published adjustments.

Can this size central air conditioning or a heat pump?

No. This calculator is for a single room air conditioner using the ENERGY STAR consumer sizing table. Central systems, mini-splits and heat pumps require a room-by-room or whole-building load calculation that accounts for construction and climate.

KEEP PLANNING
Paint CalculatorEstimate paint and primer for walls after doors, windows, coats and waste.Flooring CalculatorEstimate floor area, waste and complete boxes for plank or hardwood projects.Drywall CalculatorEstimate net wall and optional ceiling area after doors and large windows.

Plan accurately. Build safely.

This calculator is a planning estimate, not engineering or code approval. Follow manufacturer instructions and consult a qualified professional for structural, electrical, gas or permit-sensitive work.