Enter the interior volume of the RV that needs to be cooled into the calculator to estimate the air conditioner size (the calculator accepts ft³, m³, or liters).
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RV Air Conditioner Size Formula
By RV length (assumes ~8 ft width):
BTU/h = L * 8 * C * I
By interior volume (assumes ~6.5 ft ceiling):
BTU/h = (V / 6.5) * C
- L — RV length in feet
- V — interior volume in ft³
- C — climate factor (BTU per sq ft): mild 40, moderate 55, hot 68, extreme 80
- I — insulation multiplier: standard 1.15, average 1.0, 4-season 0.85
The raw BTU number is rounded up to the nearest standard rooftop unit size (5,000, 7,000, 9,500, 11,000, 13,500, or 15,000 BTU). Anything above 15,000 BTU points toward dual units. The volume mode skips the insulation factor since most users entering volume directly are working from a known interior spec.
Typical Sizes and Climate Factors
Use these as a sanity check on the calculator's recommendation.
| RV Length | Typical AC Size | Configuration |
|---|---|---|
| Under 20 ft | 5,000–9,500 BTU | Single low-profile unit |
| 20–25 ft | 11,000–13,500 BTU | Single rooftop |
| 25–32 ft | 13,500–15,000 BTU | Single rooftop |
| 32–40 ft | 2 × 13,500 BTU | Dual rooftop |
| 40 ft + | 2 × 15,000 BTU | Dual rooftop, often with heat pump |
| Outdoor Temp | Climate Factor | BTU per sq ft |
|---|---|---|
| Under 80°F | Mild | 40 |
| 80–90°F | Moderate | 55 |
| 90–100°F | Hot | 68 |
| Over 100°F | Extreme | 80 |
Example and FAQ
Example: A 28 ft travel trailer in 95°F desert heat with average insulation. Floor area is 28 × 8 = 224 sq ft. BTU need is 224 × 68 × 1.0 = 15,232 BTU/h. Round up to a 15,000 BTU rooftop unit, and add a small fan or vent fan for the bedroom if airflow is uneven.
Is one 15,000 BTU unit enough for a 35 ft RV? Usually no in hot climates. Long floorplans suffer from poor air distribution even when total BTU is adequate. Two units cool faster and give you redundancy.
Does dark exterior color matter? Yes. A dark roof in direct sun can add 10–15% to your cooling load. Pick the next climate level up if you park in full sun all day.
What about generator or shore power? A 13,500 BTU AC needs roughly 2,800–3,500 watts to start and 1,400–1,600 watts to run. A 15,000 BTU unit needs about 3,500 watts startup. A 30 amp shore connection (3,600 W max) handles one unit. Two units need 50 amp service or a soft-start kit.
Why round up to standard sizes? RV rooftop units come in fixed capacities. Undersizing means the AC runs constantly and still can't keep up on hot days.
