Popular calculators

Furnace BTUCold-climate heat pumpGarage heater BTUBTU per sq ftWindow AC BTURV mini-split sizeWhat size AC?AC cost to runAll guides →

What Size Mini-Split or Window AC?

Enter room or RV living-area dimensions. Get cooling BTU, heating estimate, and the next standard 9k / 12k / 18k / 24k size.

Space dimensions

ft
in
ft
in
ft
in

Sizing settings

Application
Insulation
Sun exposure
Climate

Your sizing estimate

Enter space dimensions to see BTU load and recommended mini-split size.

Room, window & garage calculators

Size window AC units, garage heaters, and multi-room loads — separate from RV and tiny-home mini-split pages.

Mini-split sizing by application

Pre-set insulation and load factors for RVs, tiny homes, backyard sheds, and seasonal cottages.

DIY sizing guides

View all

RV installs, tiny home insulation, she-shed comfort, cottage heat pumps, and mini-split mistakes to avoid.

DIY install

DIY Mini-Split Project Roadmap — Size, Wire, Mount & Start Up

Plan a ductless mini-split project from BTU sizing and zone selection through electrical work, placement, mounting, startup, and professional handoff.

12 min read

Mini-split calculator →

DIY install

Mini-Split Electrical Requirements — Breaker, Wire & Disconnect

DIY electrical planning for ductless mini-splits: 110V vs 220V, breaker size, wire gauge, outdoor disconnect, and when to hire an electrician.

9 min read

Mini-split calculator →

DIY install

How to Install a Window AC Safely — Support, Seal & Power

DIY window air conditioner install: sash support, brackets, sealing gaps, correct outlet circuit, and tipping hazards. Size BTU before you buy.

9 min read

Window AC calculator →

Sizing basics

BTU Per Square Foot Explained — Room Sizing Basics

How the 20–30 BTU per sq ft rule works, when to go higher or lower, and how insulation, climate, and sun exposure change your load.

9 min read

BTU calculator →

How it works

  1. 1. Measure your spaceEnter length, width, and ceiling height for each room, RV living area, or shed footprint.
  2. 2. Set application typeChoose RV, tiny home, she-shed, cottage, or standard room — insulation and BTU factors adjust automatically.
  3. 3. Buy the right BTUWe calculate cooling load, heating estimate, and round up to common mini-split sizes (9k, 12k, 18k, 24k).

FAQ

How many BTU per square foot?

Most cooled rooms need 20–30 BTU per sq ft. A 12×12 bedroom is about 3,600–4,300 BTU calculated — retail mini-splits start at 9,000 BTU. Use the BTU calculator with insulation and sun settings.

What size mini-split for an RV?

Most 25–30 ft trailers use 9,000–12,000 BTU. A 30 ft RV with 200–250 sq ft of living space often needs a 9k minimum; 12k is common in hot climates. Open the RV mini-split calculator.

What size window AC for a 12×12 room?

Calculated load is about 3,600 BTU; buy an 8,000–10,000 BTU window unit so it dehumidifies. Use the window AC calculator for other room sizes.

What size AC do I need?

Bedrooms under 200 sq ft typically take a 9,000 BTU unit. A 400 sq ft living room is usually 12,000 BTU (1 ton). Enter dimensions in what size AC do I need — this is not a Manual J permit calc.