Boiling Point of Water at Altitude Calculator
Calculate the boiling point of water from altitude or atmospheric pressure for recipe adjustments, lab planning, and high-elevation process checks.
Edited by Gail Joyce
Gail Joyce edits core chemistry calculator pages for formula clarity, unit consistency, and practical classroom and lab-use readability.
This calculator page is maintained by the Chemistry Calculators editorial team. The boiling-point relationships, pressure conversions, worked examples, and scope notes on this page are reviewed against standard chemistry reference material before major updates.
Boiling Point of Water at Altitude Calculator
Calculate the boiling point of water from a known altitude or pressure, or work backward from a measured boiling point to estimate altitude or pressure conditions.
Use this page for pure-water, open-atmosphere boiling-point estimates. It does not model dissolved solutes, pressure-cooker conditions, or mixed-liquid boiling systems.
Scope of this calculator: use it when you want the boiling point of pure water from altitude or atmospheric pressure, or when you want to estimate altitude or pressure from a measured boiling point under normal open-air conditions.
Method used: altitude is converted with a standard-atmosphere approximation, and the boiling point is then estimated for pure water from the pressure relationship. Use direct pressure input when you already have a local reading and want the closer estimate.
How to Use the Boiling Point Calculator
Follow the same order you would use in a recipe note or lab worksheet: start with the pressure or altitude you know, keep the units aligned, let the calculator solve the missing water-boiling condition, and then check whether the result fits the real environment you are modeling.
Enter altitude, pressure, or a measured boiling point
Use altitude when you are working from elevation, pressure when you already have atmospheric pressure data, or boiling point when you want to estimate the surrounding condition from a measurement.
Choose the correct unit set before solving
Switch altitude units, pressure units, and temperature units to match your source data so the calculation does not rely on mental conversions or mixed scales.
Calculate the water-only boiling-point estimate
Use the result as an estimate for pure water under atmospheric conditions. The page combines pressure relationships and Clausius-Clapeyron style boiling-point logic to do the conversion.
Review whether local conditions could shift the answer
Weather, dissolved solutes, and sealed-vessel pressure can all change the actual boiling point. Use this page for open-atmosphere water estimates, then adjust if your setup is more specialized.
Table of Contents
Quickly navigate to different sections of this guide. Click any item below to jump to that section.
Understanding Boiling Point at Altitude
The boiling point of water decreases with altitude because atmospheric pressure decreases with height. At sea level (0 m altitude), atmospheric pressure is approximately 101.325 kPa, and water boils at 100°C. As altitude increases, atmospheric pressure decreases, so water reaches its vapor pressure at a lower temperature, resulting in a lower boiling point.
The relationship between altitude and atmospheric pressure is described by the barometric formula: P = P₀ × e^(-Mgh/(RT)), where P is pressure at altitude h, P₀ is sea-level pressure, M is molar mass of air, g is gravitational acceleration, h is altitude, R is gas constant, and T is temperature. For practical purposes, a simpler approximation is often used: P = P₀ × (1 - L×h/T₀)^(gM/(RL)), where L is temperature lapse rate.
The relationship between pressure and boiling point is described by the Clausius-Clapeyron equation: ln(P₂/P₁) = -ΔH_vap/R × (1/T₂ - 1/T₁), where P is vapor pressure, T is temperature, ΔH_vap is enthalpy of vaporization, and R is gas constant. For water, ΔH_vap ≈ 40.7 kJ/mol. This equation shows that lower pressure (at higher altitude) corresponds to lower boiling point.
Understanding boiling point at altitude is crucial for cooking, laboratory work, and industrial processes. At high altitude, water boils at lower temperature, so cooking takes longer and some chemical processes behave differently. Our Boiling Point at Altitude Calculator makes these calculations instant and accurate, so you can adjust recipes and processes for altitude.
Formulas and Equations
Boiling point at altitude calculations use atmospheric pressure relationships and the Clausius-Clapeyron equation. Here's how each formula works:
Core Boiling Point Formulas
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Simple Altitude Approximation: T_b = 100 - (0.00325 × h)
Simple approximation for boiling point T_b (°C) at altitude h (meters). Accurate for altitudes up to ~3000 m. Example: At 1000 m, T_b = 100 - 3.25 = 96.75°C.
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Barometric Formula: P = P₀ × e^(-Mgh/(RT))
Exact relationship for atmospheric pressure P at altitude h, where P₀ is sea-level pressure, M is molar mass of air (~0.029 kg/mol), g is gravitational acceleration (~9.81 m/s²), R is gas constant (~8.314 J/(mol·K)), and T is temperature. More accurate but requires iterative calculation.
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Simplified Pressure-Altitude: P = P₀ × (1 - L×h/T₀)^(gM/(RL))
Simplified barometric formula using temperature lapse rate L (~0.0065 K/m) and sea-level temperature T₀ (~288 K). More practical for calculations. Example: At 1000 m, P ≈ 89.9 kPa.
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Clausius-Clapeyron Equation: ln(P₂/P₁) = -ΔH_vap/R × (1/T₂ - 1/T₁)
Relates vapor pressure to temperature, where P is vapor pressure, T is temperature (K), ΔH_vap is enthalpy of vaporization (~40.7 kJ/mol for water), and R is gas constant. Used to find boiling point from pressure.
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Boiling Point from Pressure: T_b = 1 / (1/T₀ - (R/ΔH_vap) × ln(P/P₀))
Calculate boiling point T_b (K) from pressure P, where T₀ is reference boiling point (373.15 K for water at 101.325 kPa), P₀ is reference pressure (101.325 kPa), ΔH_vap is enthalpy of vaporization, and R is gas constant. This is derived from Clausius-Clapeyron equation.
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Altitude from Pressure: h = (RT₀/(gM)) × ln(P₀/P)
Calculate altitude h (m) from atmospheric pressure P, using barometric formula. Useful for reverse calculations. Requires known sea-level pressure P₀ and temperature T₀.
Worked Examples
Let's work through detailed examples showing how to calculate boiling point at altitude step by step. These examples cover common altitude scenarios.
Example 1: Calculate Boiling Point at 1000 m Altitude
Scenario: What is the boiling point of water at 1000 m altitude?
Solution:
Step 1: Use simple approximation
T_b = 100 - (0.00325 × h) = 100 - (0.00325 × 1000)
T_b = 100 - 3.25 = 96.75°C
Step 2: More accurate calculation using pressure
At 1000 m, P ≈ 89.9 kPa (from barometric formula)
Using Clausius-Clapeyron: T_b ≈ 96.7°C
Answer: Boiling point ≈ 96.7°C at 1000 m altitude
Example 2: Calculate Boiling Point from Pressure
Scenario: Atmospheric pressure is 70 kPa. What is the boiling point of water?
Solution:
Step 1: Use Clausius-Clapeyron equation
ln(P₂/P₁) = -ΔH_vap/R × (1/T₂ - 1/T₁)
P₁ = 101.325 kPa, T₁ = 373.15 K (100°C)
P₂ = 70 kPa, T₂ = ?
ln(70/101.325) = -40700/8.314 × (1/T₂ - 1/373.15)
T₂ ≈ 363.2 K = 90.0°C
Answer: Boiling point ≈ 90.0°C at 70 kPa pressure
Example 3: Calculate Altitude from Boiling Point
Scenario: Water boils at 90°C. What is the approximate altitude?
Solution:
Step 1: Use simple approximation
T_b = 100 - (0.00325 × h)
90 = 100 - (0.00325 × h)
h = (100 - 90) / 0.00325 ≈ 3077 m
Answer: Approximate altitude ≈ 3077 m (about 10,000 feet)
Frequently Asked Questions (FAQs)
Here are the main questions users ask when converting between altitude, pressure, and the boiling point of pure water.
How does altitude affect boiling point?
Boiling point decreases with altitude because atmospheric pressure decreases. At sea level (0 m), water boils at 100°C. At 1000 m altitude, water boils at approximately 96.7°C. At 3000 m altitude, water boils at approximately 90°C. This is because lower pressure means less energy is needed to overcome atmospheric pressure and form vapor bubbles. Our Boiling Point at Altitude Calculator helps you quickly determine boiling point for any altitude.
How do I calculate boiling point from altitude?
Use the relationship: T_b = 100 - (0.00325 × altitude), where T_b is boiling point in °C and altitude is in meters. More accurately, use: P = P₀ × (1 - L×h/T₀)^(gM/(RL)), where P is pressure at altitude h, then use Clausius-Clapeyron equation to find boiling point. Our calculator handles all conversions automatically.
Why does water boil at lower temperature at high altitude?
Water boils when vapor pressure equals atmospheric pressure. At high altitude, atmospheric pressure is lower, so water reaches its vapor pressure at a lower temperature. This is why cooking takes longer at high altitude—water boils at lower temperature, so food cooks slower. Lower pressure means less energy needed to form vapor bubbles.
How does atmospheric pressure affect boiling point?
Boiling point increases with atmospheric pressure. At standard atmospheric pressure (101.325 kPa), water boils at 100°C. At higher pressure (e.g., in pressure cooker at 200 kPa), water boils at ~120°C. At lower pressure (e.g., at high altitude at 70 kPa), water boils at ~90°C. This relationship is described by the Clausius-Clapeyron equation.
How do I calculate altitude from boiling point?
Use simple approximation: h = (100 - T_b) / 0.00325, where h is altitude in meters and T_b is boiling point in °C. More accurately, first find pressure from boiling point using Clausius-Clapeyron equation, then find altitude from pressure using barometric formula. Our calculator handles all conversions automatically.
What is the boiling point at Mount Everest?
At Mount Everest summit (8848 m altitude), atmospheric pressure is approximately 33.7 kPa, and water boils at approximately 71°C. This is why climbers need special cooking equipment—normal stoves don't work well because water boils at such low temperature. Pressure cookers are essential for high-altitude cooking.
How accurate is the simple approximation formula?
The simple approximation T_b = 100 - (0.00325 × h) is accurate to within ~1°C for altitudes up to ~3000 m. For higher altitudes or more precision, use barometric formula and Clausius-Clapeyron equation. Our calculator uses accurate formulas for all calculations, ensuring precision at any altitude.
How do I account for local weather conditions?
Local weather conditions affect atmospheric pressure. High-pressure systems increase pressure, raising boiling point. Low-pressure systems decrease pressure, lowering boiling point. For precise calculations, use actual measured pressure rather than calculated pressure from altitude. Our calculator accepts both altitude and pressure inputs, so you can use measured pressure for accuracy.
Does this page work for salt water or other liquids?
No. This page is for pure water under open-atmosphere conditions. Dissolved solutes, pressure-cooker setups, and other liquids shift the boiling point, so those cases need different models or reference data.
References and Further Reading
For more in-depth information about boiling point at altitude, atmospheric pressure, and related topics, consult these authoritative sources:
| Resource | Description | Category |
|---|---|---|
| NIST Chemistry WebBook: Water | Reference data for water properties used when checking vapor-pressure and phase-change values | Reference Data |
| ChemLibreTexts: Clausius-Clapeyron Equation | Explains the pressure-temperature relationship behind boiling-point changes | Physical Chemistry |
| Atkins, P., et al. (2017). Physical Chemistry | Detailed coverage of boiling point and Clausius-Clapeyron equation | Textbook |
| Cengel, Y. A., & Boles, M. A. (2014). Thermodynamics: An Engineering Approach | Engineering perspective on boiling point and pressure relationships | Textbook |
| Khan Academy: Chemistry | Free educational content on boiling point and phase transitions | General Chemistry |