Mini Split BTU Calculator: Size Any Room in Four Steps
No email gate, no app: the four-step sizing calculation, worked examples, and the cheapest verified system in every BTU class as the starting point for each size. Our dataset holds 6 verified system(s) here, 6 with first-hand prices from $659 to $5,970; the cheapest is the Klimaire KSIE 12k.
Computed from our dataset
- 6 system(s) from our verified dataset appear on this page.
- Price range: $659 to $5,970 (verified 2026-11-04).
- Cheapest: Klimaire KSIE 12k at $659 (Heat & Cool).
- Highest SEER2: MRCOOL DIY 5th Gen 5-Zone 48k (6+9+9+9+12) at 21.8 SEER2.
- Best heating rating: Senville LETO 9k, rated to 5°F.
| System | Zones | BTU | Coverage | SEER2 | Heats to | Install | Price | |
|---|---|---|---|---|---|---|---|---|
| Klimaire KSIE 12k KSIE012-H120-O / KSIE012-H120-IW-2 | 1 | 12,000 | 550 sq ft | — | 5°F | Pro / flare | $659$969 at Heat & Cool | Check price |
| Senville LETO 9k SENL-09CD/220 | 1 | 9,000 | — | 21.2 | 5°F | Pro / flare | $799.99 at Senville | Check price |
| Senville LETO 18k SENL-18CD | 1 | 18,000 | 700-1,000 sq ft | 19.2 | 5°F | Pro / flare | $999.99 at Senville | Check price |
| Senville LETO 24k SENL-24CD | 1 | 24,000 | 1,000-1,250 sq ft | 18.7 | 5°F | Pro / flare | $1,249.99 at Senville | Check price |
| MRCOOL DIY 5th Gen 36k DIY-36-HP-WM-230D25-O | 1 | 36,000 | up to 1,550 sq ft | 18 | — | Pro / flare | $3,469 at Sylvane | Check price |
| MRCOOL DIY 5th Gen 5-Zone 48k (6+9+9+9+12) DIY-MULTI6-48HP-230 | 5 | 48,000 | Per-zone: 250-600 sq ft | 21.8 | — | Pro / flare | $5,970 at HVACDirect | Check price at HVACDirect |
The calculation
1. Measure the space (length x width). 2. Multiply by 20 for the baseline BTU need (25 for sunny, poorly insulated, or high-ceiling spaces; 30-35 for sunrooms). 3. Round up to the nearest standard class: 9k, 12k, 18k, 24k, 36k, 48k. 4. Shop inside that class - the table below is the cheapest verified system in each class, and every class page lists the full field.
Worked examples
- 400 sq ft bedroom: 400 x 20 = 8,000 BTU -> 9,000 or 12,000 class.
- 750 sq ft living space: 750 x 20 = 15,000 BTU -> 18,000 class.
- 1,200 sq ft open floor: 1,200 x 20 = 24,000 BTU -> 24,000 class.
- 400 sq ft sunroom: 400 x 32 = 12,800 BTU -> 18,000 class (sunroom uprate).
Buying notes
- A load calculation (Manual J) beats any rule of thumb for a whole-house project; this calculator is for single rooms and open spaces, which is most mini split projects.