What Size Mini Split Do I Need? Room-by-Room Guide
Choosing the right size mini split system is one of the most important steps to getting great performance and energy savings. A system that’s too small will struggle to keep you comfortable, while one that’s too big will cycle on and off too much, wasting energy and wearing down faster. So how do you know what size you need? Here’s a clear, room-by-room guide to help Missouri homeowners get it right in 2025.
8/6/20252 min read
Mini Split Sizing Basics
Mini splits are sized in BTUs (British Thermal Units) — a measurement of heating or cooling power.
As a general rule:
Smaller rooms (100–400 sq ft) need 9,000–12,000 BTUs
Medium rooms (400–700 sq ft) need 12,000–18,000 BTUs
Large rooms (700–1,000+ sq ft) may need 18,000–24,000+ BTUs
But it’s not just about square footage — insulation, ceiling height, sun exposure, and windows also matter.
Room-by-Room BTU Guide
Living Room (400–800 sq ft):
Most Missouri living rooms fall in this range. You’ll typically need a 12,000 to 18,000 BTU unit.
Bedroom (150–350 sq ft):
Bedrooms often work well with 9,000 to 12,000 BTUs, especially if there’s good insulation and a single window.
Kitchen (250–500 sq ft):
Because kitchens produce extra heat from cooking, go one size up. A 12,000 to 15,000 BTU unit is common.
Garage or Basement (400–700 sq ft):
These areas often have poor insulation. You’ll want 15,000 to 18,000 BTUs, or even more depending on ceiling height.
Sunroom or Additions (200–500 sq ft):
These are notorious for temperature swings. Go higher: 12,000 to 18,000 BTUs, depending on exposure.
Multi-Zone Sizing Example
If you're installing a multi-zone system (one outdoor unit powering several indoor units), you'll size each room individually. For example:
Living Room: 18,000 BTU
Bedroom 1: 9,000 BTU
Bedroom 2: 9,000 BTU
Kitchen: 12,000 BTU
Total: 48,000 BTUs (usually served by a 4-ton outdoor unit)
Expert Tip: Don’t Guess
It’s always best to have a licensed installer assess your home. A proper load calculation takes into account more than just square footage—it includes insulation levels, ceiling heights, sun direction, number of people, and more.
Common Mistake: Oversizing
Many homeowners think “bigger is better,” but that leads to:
Short cycling (turning on and off too quickly)
Uneven temperature control
Higher electricity bills
Shorter system lifespan
Proper sizing means better comfort and lower energy use.
Summary
Mini split sizing isn’t one-size-fits-all. It depends on the layout and demands of each space. Getting it right means enjoying long-term efficiency, quieter operation, and fewer issues down the road.
Need help choosing the right size system? Global Kingdom Contracting offers free sizing consultations for homeowners in the St. Louis area. Call 636-222-3509 to schedule yours today.