Weather apps give you a number. What they don't tell you is whether you need a jacket, whether it's safe to run outside, or whether your kids can play in the yard. This guide fills in the gap.

Temperature thresholds are fairly consistent across healthy adults, though age, health conditions, humidity, wind, and sun exposure all shift the limits. The ranges below are general guidance, not medical advice — but they're a useful mental map for everyday decisions.

Cold Temperatures: What to Wear and When to Be Careful

10–20°C (50–68°F): Cool and comfortable

This is one of the most comfortable ranges for outdoor activity. You'll probably want a light jacket or long sleeves in the morning or evening, but midday can feel warm in the sun. Most people are fine in a single layer during exercise.

Great conditions for running, cycling, hiking, or any sustained outdoor activity. You won't overheat, and the cool air is easy on your lungs.

0–10°C (32–50°F): Cold — layers needed

At this range, you want a proper jacket, and if you're staying still (watching a game, waiting for transport, standing outdoors), you'll feel it. Wind makes a big difference here — a still 5°C day is much more comfortable than a windy one.

For exercise: dress in layers. A base layer that wicks moisture plus a mid-layer and windproof outer shell is the standard approach. Exposed skin on hands and ears will get cold; gloves and a hat make a real difference.

Hypothermia risk at this temperature range is low for healthy adults who are active and dry, but rises quickly if someone is wet, sedentary, or has limited mobility.

-10–0°C (14–32°F): Very cold — full winter gear

Below freezing but above -10°C is typical winter weather in temperate climates. You need insulated winter clothing — a proper coat, hat, gloves, scarf, warm socks, and insulated footwear.

Exposed skin will feel uncomfortable within minutes in wind. Wind chill at -5°C with a 20 km/h wind feels like -12°C. Check the "feels like" temperature, not just the actual reading.

For exercise: still fine if you're well dressed, but be aware that inhaling very cold air can trigger symptoms in people with asthma or respiratory conditions. Cover your mouth with a buff or balaclava.

Use the temperature converter if you're reading a forecast in unfamiliar units — a -5°C forecast is 23°F, which makes more intuitive sense to US readers as "below freezing."

Below -10°C (14°F): Dangerous cold — limit exposure

At these temperatures, frostbite on exposed skin can occur within 30 minutes in wind. At -20°C (-4°F) with moderate wind, exposed skin can freeze in 10–15 minutes.

Rules of thumb for this range:

• Cover all skin. No exposed wrists, no uncovered ears, nothing showing between gloves and sleeve.
• Layering matters more than any single item of clothing.
• Keep activity levels high if you're outside — stopping to rest in extreme cold allows your body temperature to drop quickly.
• Know the signs of hypothermia: shivering, confusion, slurred speech, loss of coordination. Get indoors and warm up.

Children and elderly people reach dangerous body temperatures faster than healthy adults. At these temperatures, limit outdoor exposure for vulnerable groups.

Hot Temperatures: When Comfort Becomes Risk

20–30°C (68–86°F): Warm to hot — comfortable for most

The classic "nice day" range. Most people are comfortable in light clothing. Sustained exercise gets more demanding as you approach 30°C, particularly in direct sun.

Hydration matters more in this range than people often realize. Thirst is a lagging indicator — if you're active outdoors, drink before you feel thirsty.

30–35°C (86–95°F): Hot — modify activity

At 30°C+, outdoor exercise becomes significantly more physiologically demanding. Your body is working harder to cool itself, heart rate runs higher for the same effort, and performance drops.

Practical adjustments: move vigorous activity to early morning or evening, stay in shade during peak sun hours (typically 11am–3pm), wear light and loose clothing, and increase fluid intake. Sunscreen matters — sunburn reduces your skin's ability to cool itself.

For vulnerable groups (elderly, young children, people with heart conditions), sustained exposure above 32°C warrants careful management.

35–40°C (95–104°F): Very hot — heat exhaustion risk

This is the range where heat exhaustion becomes a real risk for otherwise healthy adults who aren't acclimatized. Symptoms include heavy sweating, cold and clammy skin, weakness, and dizziness. Move to a cool environment, drink fluids, and rest.

Don't leave children or animals in parked cars. Even on a 30°C day, car interiors can reach 50°C+ within minutes.

If you're doing any physical work outdoors in this range, take mandatory rest breaks in shade and maintain aggressive hydration.

Above 40°C (104°F): Dangerous — heat stroke risk

At 40°C+, heat stroke becomes a genuine threat, particularly with physical exertion. Heat stroke is a medical emergency — body temperature above 40°C (104°F), confusion, hot dry skin (sweating may have stopped), rapid heart rate.

Healthy adults should limit strenuous outdoor activity at these temperatures. For high-risk groups, outdoor exposure should be minimized entirely during peak heat.

Humidity: Why "Feels Like" Matters More Than the Thermometer

Air temperature tells you one thing; humidity tells you another. High humidity reduces your body's ability to cool itself through sweat evaporation, which makes hot days feel significantly hotter — and more dangerous.

The "heat index" (or "apparent temperature") accounts for both. At 35°C with 80% humidity, the heat index is approximately 46°C — well into dangerous territory. At 35°C with 20% humidity, it's about 37°C — still hot, but much more manageable.

The inverse is also true: cold temperatures with high wind feel much colder than the thermometer reads (wind chill). A thermometer reading of -5°C with a 30 km/h wind has a wind chill equivalent of about -14°C.

When making decisions about outdoor activities in temperature extremes, always check the "feels like" figure rather than just the air temperature.

Quick Reference: Dressing for Temperature

Use the temperature converter to check any forecast in Celsius or Fahrenheit and build a consistent mental reference for both scales.