Mini Split Sizing Calculator
BTU size for a ductless mini split from room size and conditions.
Enter your values
Enter the room area in sq ft.
Enter the ceiling height in ft.
Choose one of: Well insulated / new, Average, Poor / older home.
Choose one of: Shaded, Average, Very sunny.
Enter the regular occupants you are working with.
Choose one of: No, Yes.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Recommended unit
- 9,000 BTU/hr (0.8 ton)
- Calculated load
- 8,000 BTU/hr
- Load per sq ft
- 20 BTU/hr-ft2
Working
- 1400 ft2 x 20 x 1 x 1 x 1 = 8,000 BTU/hr
Quick answer
Start with about 20 BTU per square foot, then adjust for ceiling height, insulation quality, sun exposure, occupants and kitchen heat.
BTU = area x 20 x height factor x insulation factor + adders
At a glance
| What it does | BTU size for a ductless mini split from room size and conditions. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Room area, Ceiling height, Insulation, Sun exposure, Regular occupants, Kitchen in this space |
| Main output | Recommended unit |
| Formula | BTU = area x 20 x height factor x insulation factor + adders |
| Cost | Free — no sign-up, no download |
How to use the Mini Split Sizing Calculator
- 1Enter the room area and true ceiling height.
- 2Adjust for insulation and sun - a west-facing glass wall changes the answer a lot.
- 3Round up to the next standard head size, but avoid oversizing by more than one step.
Inputs explained
- Room area(sq ft)
- Enter the room area in sq ft.
- Ceiling height(ft)
- Enter the ceiling height in ft.
- Insulation
- Choose one of: Well insulated / new, Average, Poor / older home.
- Sun exposure
- Choose one of: Shaded, Average, Very sunny.
- Regular occupants
- Enter the regular occupants you are working with.
- Kitchen in this space
- Choose one of: No, Yes.
Worked example
Using the values the calculator loads with:
Inputs
- Room area400 sq ft
- Ceiling height8 ft
- InsulationAverage
- Sun exposureAverage
- Regular occupants2
- Kitchen in this spaceNo
Results
- Recommended unit9,000 BTU/hr (0.8 ton)
- Calculated load8,000 BTU/hr
- Load per sq ft20 BTU/hr-ft2
- 400 ft2 x 20 x 1 x 1 x 1 = 8,000 BTU/hr
Frequently asked questions
Is bigger always better?
No. An oversized mini split short-cycles, never runs long enough to dehumidify, and leaves the room clammy. Sizing close to the load is what makes inverter units efficient.
Does this replace a Manual J?
It is a fast planning estimate. For a whole-house system or a tight budget, a proper Manual J load calculation is still the gold standard.
What do I need to enter into the Mini Split Sizing Calculator?
Just 6 values: room area, ceiling height, insulation, sun exposure, regular occupants, kitchen in this space. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Mini Split Sizing Calculator work out the answer?
Start with about 20 BTU per square foot, then adjust for ceiling height, insulation quality, sun exposure, occupants and kitchen heat. It applies the formula BTU = area x 20 x height factor x insulation factor + adders and shows the working so you can check each step by hand.
Is the Mini Split Sizing Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.