BTU Calculator
ASHRAE-compliant room load calculator · No sign-up required
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All Guides
BTU Calculators for Every Space
Each guide uses room-specific load factors — not generic formulas. Find your space and get a tailored BTU recommendation.
By Room Type
Specialty Spaces
Server Room
24/7 equipment load
RV / Camper
Shore power limits
Tiny House
Loft stratification
Portable AC
SACC vs labeled BTU
Studio Apt.
Open plan sizing
1-Bed Apt.
One unit or two?
2-Bed Apt.
Zone-by-zone sizing
Basement Apt.
Humidity control
Attic Room
Roof solar gain
Sunroom
Glass wall SHGC
Workshop
High ceilings + tools
Gym / Workout
Metabolic heat load
Classroom
30+ occupant load
12K BTU Coverage
What sq ft does it cool?
BTU Per Sq Ft
Room-by-room rates
FAQ
Common Questions, Answered
Real sizing questions from homeowners — with the reasoning behind each answer.
What AC unit should I get for a sunny 550 sqft apartment in California?
Horizontal slider windows, lots of sun, and 550 sqft in CA? Here's exactly which AC type and BTU rating to buy — and how to keep your electricity bill low.
What AC tonnage do I need for a 15×30 room on the top floor?
Top-floor 15×30 room with one northeast-facing wall and no direct sun? Find out why 1 ton (12,000 BTU) is the right call, and how kitchens, sunlight, and occupancy change that number.
How do I pick the right size AC for a small bedroom or office?
Buying the smallest AC available is a mistake. For 150–250 sqft rooms, the right BTU depends on sun exposure, equipment heat, and ceiling height. Here's the full guide.
Is a higher BTU air conditioner always better if the wattage is similar?
A higher-BTU unit at similar wattage sounds like a deal, but for small rooms it causes short cycling, humidity problems, and higher bills. Here's why an inverter wins.