Portable AC BTU by Room Size: SACC Sizing Chart

Sizing a portable air conditioner is about matching SACC capacity to your room — not the inflated ASHRAE headline number. Undersize and the room never gets comfortable; oversize and the unit short-cycles, leaving the air clammy. Use the chart below as a starting point.

SACC Sizing Chart

Room size	Baseline SACC BTU
150 sq ft (small bedroom)	5,000–6,000
250 sq ft (bedroom / office)	7,000–8,000
350 sq ft (living room)	8,000–10,000
450 sq ft (large living room)	10,000–12,000
550+ sq ft (open plan)	12,000–14,000+

The rule of thumb is roughly 20 SACC BTU per square foot, then adjust.

Adjustments

• Sunny / west-facing room: add about 10%.
• Kitchen or heat-producing equipment: add about 4,000 BTU.
• High ceilings (above 8 ft): add about 10–15%.
• Heavily shaded room: subtract about 10%.

Why You Should Size Up, Not Down

Portable ACs lose real capacity to the exhaust hose and (for single-hose units) to negative pressure. Because the SACC figure already bakes in some of this, but real installations vary, it is safer to round up a tier than to undersize. An undersized unit runs constantly and still loses.

Remember to use the SACC number — see why in our SACC vs ASHRAE explainer — and consider single vs dual hose before buying. Full context in the main buying guide.

FAQ

How many BTU do I need for a 300 sq ft room?

Around 8,000–9,000 SACC BTU for a standard 300 sq ft room, then add capacity if it is sunny, has high ceilings, or is a kitchen.

Is it better to oversize or undersize a portable AC?

Round up rather than down. Portable ACs lose efficiency to the exhaust hose, so a slightly larger SACC rating gives margin. Extreme oversizing causes short-cycling and a clammy feel, so move up one tier, not several.

Does ceiling height affect BTU needs?

Yes. Standard charts assume 8 ft ceilings. For higher ceilings add roughly 10–15% because there is more air volume to cool.