Barometric pressure, also called atmospheric pressure, is the measure of the weight of Earth’s atmosphere. The atmosphere has five layers: exosphere, thermosphere, mesosphere, stratosphere, and troposphere, which is the layer closest to the Earth’s surface. Barometric pressure increases as altitude decreases, with air molecules in the upper layers compressing the layers below them. Barometric pressure fluctuates based on elevation levels, wind patterns, and temperatures.

Barometric pressure is measured either in standard atmospheres (atm), Pascals (Pa), inches of mercury (inHg), or bars (bar). At sea level, the normal range for barometric pressure is:

• Between 1 atm and 0.986923 atms
• Between 101,325 Pa and 100,000 Pa
• Between 31 inHg and 29 inHg
• Between 1.01325 bars and 1 bar

Barometric pressure is essential to understand because it affects our daily lives.

1. It helps you understand weather patterns. Barometric pressure changes every day due to wind patterns, air temperatures, and the Earth’s rotation. When these variables create a high-pressure system, the air presses closer to the Earth’s surface, where the temperature is warmer and the air can sustain higher levels of water vapor levels—resulting in a warmer, clearer day. In a low-pressure system, the air congregates higher up in the atmosphere, where the temperature is cooler and less capable of holding water vapor—resulting in a cold-weather day with a higher chance of precipitation. Thus, higher pressure is indicative of calm weather, while low barometric pressure indicates poor weather. Meteorologists and sailors use fluctuations in barometric pressure to forecast weather conditions.

2. It impacts your oxygen levels. Ragged breathing at higher altitudes is a result of low barometric pressure. The air molecules in lower-pressure altitudes (for instance, on a mountaintop) are less dense because they’re not being pushed together by as much barometric pressure, resulting in fewer oxygen molecules per breath. In high-pressure areas near sea level, it’s easier for your lungs to absorb oxygen because gravity forces the air down to you. In low-pressure areas, there’s less force pushing oxygen toward you, so your lungs may struggle to absorb it. This is why climbers traveling to the top of Mount Everest or other high altitudes have to take it slow and acclimate to their environment—if they don’t, the air pressure change will shock their bodies, and their lungs will not be able to find or absorb oxygen fast enough.

3. It can affect scientific experiments. Barometric pressure affects everything from temperature to humidity to evaporation. When conducting experiments, scientists must record barometric pressure in the lab to ensure that they can perfectly replicate their experiment. The lab can send their barometric pressure readings to other labs that are conducting similar experiments.

4. It can impact baking. Barometric pressure directly impacts how quickly fluids evaporate, which has a significant effect on baking. Evaporation slows under high pressure, meaning that cakes and breads take longer to rise and require more time in the oven before they’re finished baking. In lower-pressure environments, evaporation happens quicker, so cakes and breads rise more quickly and finish baking faster.