Air conditioner BTU calculator

Air conditioner size for a room in BTU/h, tons and kW from floor area, ceiling height, insulation, sun and occupants, beside the Energy Star chart.

Mis à jour 28 septembre 2026Exemples vérifiés : 4

Cooling load

BTU/h

Nombre entier ; Au plus proche, égalités en s’éloignant de zéro

Cooling load: 0.5tons / 1.76kW
Next common unit size: 6,000BTU/h
Energy Star chart for this area: 8,000BTU/h

This is a rule-of-thumb estimate. For a whole house or an unusual room, a Manual J load calculation is the reliable method.

By the rule of thumb the room needs about 6,000 BTU/h (0.5 tons, 1.76 kW), so look at 6,000 BTU/h units. The Energy Star chart suggests 8,000 BTU/h for the same floor area.

Where the load falls among common unit sizes (BTU/h)

Comment le calcul est effectué S

Base load (rule of thumb)
$300\ \text{ft}^2 \times 20 = 6{,}000\ \text{BTU/h}$
About 20 BTU/h per ft² for an 8 ft ceiling (27.87 m²), this calculator's rule of thumb. The Energy Star chart gives 8,000 BTU/h for this area, 26.7 per ft².
Ceiling height and insulation
$6{,}000 \times \frac{8}{8} \times 1 = 6{,}000$
Scaled by room volume; the insulation factors (good 0.9, average 1.0, poor 1.2) are this calculator's assumption.
Sun (Energy Star)
$6{,}000 \times 1 = 6{,}000$
People and kitchen (Energy Star)
$+ 600 \times 0 + 0 = 6{,}000\ \text{BTU/h}$
Tons and kilowatts
$\frac{6{,}000}{12{,}000} = 0.5\ \text{tons},\quad 6{,}000 \times 0.293071 \div 1000 = 1.758426\ \text{kW}$

À propos de Air conditioner BTU calculator

The cooling load starts at 20 BTU/h per square foot for an 8 ft ceiling, scales with ceiling height and an insulation factor, then takes Energy Star's room air conditioner adjustments: 10% less for a heavily shaded room, 10% more for a very sunny one, 600 BTU/h for each regular occupant beyond two and 4,000 BTU/h for a kitchen. The load is also given in tons (12,000 BTU/h each) and kW, with the next common unit size.

A 300 ft² room with an 8 ft ceiling and average conditions comes to 6,000 BTU/h, half a ton or 1.76 kW. Energy Star's sizing chart, based on 8 ft ceilings, lists 8,000 BTU/h for 300 up to 350 ft², so its figure is shown alongside for rooms of 100 to 2,500 ft².

Both are estimates for one room. For a whole house, ACCA describes its Manual J as the ANSI-recognised method for equipment sizing loads.

Exemples détaillés

300 ft² room, 8 ft ceiling, average everything

Surface d’une pièce: 300 ft²
Ceiling height: 8 ft
Insulation: Moyenne
Sun exposure: Normal
People who regularly use the room: 2

Cooling load: 6,000 BTU/h
Cooling load: 0.5 tons
Cooling load: 1.76 kW
Next common unit size: 6,000 BTU/h
Energy Star chart for this area: 8,000 BTU/h

Source de vérification : Python decimal: 300 × 20 = 6,000 BTU/h ÷ 12,000 = 0.5 ton × 0.29307 = 1.758 kW; Energy Star chart row 300–350 ft² = 8,000

Sunny 400 ft² kitchen, 10 ft ceiling, poor insulation, 4 people

Surface d’une pièce: 400 ft²
Ceiling height: 10 ft
Insulation: Poor
Sun exposure: Very sunny
People who regularly use the room: 4
The room is a kitchen: oui

Cooling load: 18,400 BTU/h
Cooling load: 1.53 tons
Next common unit size: 24,000 BTU/h
Energy Star chart for this area: 16,200 BTU/h

Source de vérification : Python decimal: 400 × 20 × 1.25 × 1.2 × 1.1 + 2 × 600 + 4,000 = 18,400; Energy Star 10,000 × 1.1 + 1,200 + 4,000 = 16,200

Shaded 20 m² bedroom, 2.4 m ceiling, good insulation, 1 person

Surface d’une pièce: 20 m²
Ceiling height: 2.4 m
Insulation: Good
Sun exposure: Heavily shaded
People who regularly use the room: 1

Cooling load: 3,433 BTU/h
Next common unit size: 5,000 BTU/h
Energy Star chart for this area: 5,400 BTU/h

Source de vérification : Python decimal: 215.28 ft² × 20 × (7.874/8) × 0.9 × 0.9 = 3,432.6 BTU/h; one occupant adds nothing; chart 6,000 × 0.9

Edge: 150 ft² sits on a chart boundary

Surface d’une pièce: 150 ft²
Ceiling height: 8 ft
Insulation: Moyenne
Sun exposure: Normal
People who regularly use the room: 2

Cooling load: 3,000 BTU/h
Energy Star chart for this area: 6,000 BTU/h

Source de vérification : Energy Star chart: 150 ft² falls in the “150 up to 250” row (6,000 BTU/h); rule of thumb 150 × 20 = 3,000

Questions

What size air conditioner do I need for my room?

Energy Star's chart for 8 ft ceilings lists 5,000 BTU/h for 100–150 ft², 6,000 for 150–250 ft², 8,000 for 300–350 ft², 10,000 for 400–450 ft², 12,000 for 450–550 ft² and 18,000 for 700–1,000 ft². The 20 BTU/h per ft² rule gives less for small rooms, 6,000 against 8,000 at 300 ft², so the chart figure is shown beside the result.

How many BTU per square foot do I need?

This calculator uses 20 BTU/h per square foot for an 8 ft ceiling. Energy Star's chart works out higher for small and mid-sized rooms: 8,000 BTU/h for 300 ft² is about 27 per ft², and 12,000 BTU/h for 450 ft² is also about 27. At 1,000 ft² the chart's 21,000 BTU/h is 21 per ft², close to the rule.

How many BTU is a ton of air conditioning?

One ton of refrigeration is 12,000 BTU/h, which NIST SP 811 lists as 3,516.853 W; one BTU/h is 0.2930711 W. A 6,000 BTU/h room unit is therefore half a ton or 1.76 kW of cooling, and a 24,000 BTU/h split system is 2 tons or 7.03 kW.

Is a bigger air conditioner better?

No. Energy Star says an oversized unit costs more to buy, wastes energy and does not cool better: it cools the room before it has time to remove the humidity, leaving the air damp and clammy. Choose the unit size that matches the load rather than rounding up by a full size or more for safety.

How do ceiling height and sunlight change the BTU needed?

Energy Star's chart assumes 8 ft ceilings, and this calculator scales the load in proportion to height, so a 10 ft ceiling adds 25%. Energy Star advises 10% less capacity for a heavily shaded room and 10% more for a very sunny one, plus 600 BTU/h for each regular occupant beyond two and 4,000 BTU/h in a kitchen.

Quelle est la précision de « Air conditioner BTU calculator » ?

La précision dépend de vos données et des hypothèses de la méthode. Le calcul décimal utilise 50 chiffres significatifs, mais les estimations, méthodes numériques et données sources peuvent être moins précises ; l’arrondi affiché ne supprime pas ces limites. Exemples résolus vérifiés à partir de sources indépendantes : 4. Par exemple, « 300 ft² room, 8 ft ceiling, average everything » est vérifié à l’aide de Python decimal: 300 × 20 = 6,000 BTU/h ÷ 12,000 = 0.5 ton × 0.29307 = 1.758 kW; Energy Star chart row 300–350 ft² = 8,000.

D’où vient cette méthode ?

ENERGY STAR — Room air conditioners: sizing chart and adjustments; ACCA Manual J 8th Edition (ANSI/ACCA 2 Manual J – 2016) — residential load calculation; NIST SP 811 Appendix B.9 — ton of refrigeration and BTU/h to watt.

À propos de ce calculateur

Q = 20\,A\,\frac{h}{8}\,f_{\text{ins}}\,f_{\text{sun}} + 600\max(0, p - 2) + 4000\,[\text{kitchen}]

Sources

Vérifié avec les références

Ce calculateur comprend 4 exemples résolus dont les réponses proviennent de sources indépendantes. Ils font partie de la suite de tests et peuvent aussi être exécutés ici.

Where the load falls among common unit sizes (BTU/h)

Base load (rule of thumb)

Ceiling height and insulation

Sun (Energy Star)

People and kitchen (Energy Star)

Tons and kilowatts