Want a Grow Sensor?
Get early access to the now.

Vapour pressure calculator and step-by-step guide

Lucy Starley
November 16, 2023
8 min read
Large cannabis fan leaf that is a good candidate for removal via defoliation
Large cannabis fan leaf that is a good candidate for removal via defoliation
Download your free VPD calculator
Oops! Something went wrong while submitting the form.

Are you ready to take your cultivation skills to the next level? Well, get ready because we’re about to dive into the fascinating world of vapour pressure calculation! In this detailed guide, we’ll share the knowledge you need to understand and master the art of calculating vapour pressure.

Now, you might be wondering, “What’s the big deal with vapour pressure?” Well, my friend, vapour pressure is a critical factor that can make or break your cannabis plants’ growth and overall health. It’s a secret weapon in your arsenal that ensures your plants receive the optimal environment they need to thrive!

In this article, we’ll explore the concept of vapour pressure and how it relates to temperature and humidity. We’ll also uncover the significance of maintaining the right vapour pressure levels for your beloved green beauties. But here’s the best part: we’re going to equip you with a powerful tool—the vapour pressure calculator. This will enable you to precisely measure and monitor this crucial parameter!

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis you’re doing so in accordance with the law and subject to appropriate permissions and licenses of the applicable country.

What is vapour pressure?

Alright, let’s get down to the nitty-gritty of vapour pressure and why it matters in the world of cannabis cultivation. Understanding this concept is key to providing your plants with the ideal growing conditions they need to reach their full potential. So, buckle up and prepare for some enlightening insights!

Explaining the concept of vapour pressure

Picture this: you’re sipping a hot cup of tea, and steam rises from the surface. Ever wondered what causes that steam? Well, that’s where vapour pressure comes into play.

Vapour pressure is the force exerted by water molecules as they evaporate into the air. The higher the temperature, the more water molecules gain energy and escape into the atmosphere. This process affects the humidity levels and has a direct impact on your cannabis plants.

A macro shot of a cannabis leaf.

Why is vapour pressure important in cannabis cultivation?

Now, you might be wondering, “Why should I care about vapour pressure when growing cannabis?” Well, vapour pressure plays a crucial role in your plants’ lives! It influences their transpiration process—the movement of water from the roots, through the plant, and into the air.

When the vapour pressure in the air surrounding your plants is lower than the pressure in the leaves, water molecules escape through tiny openings called stomata. This transpiration process is essential for nutrient uptake, plant cooling, and overall growth. Without the right vapour pressure, your plants might struggle to absorb nutrients efficiently or even become susceptible to stress-related issues.

Maintaining the best vapour pressure in your grow space is like creating a spa-like retreat for your plants! By striking the perfect balance, you ensure that they have a comfortable environment to thrive in. But what happens if the vapour pressure is too high or too low? Let’s learn more!

Consequences of high or low vapour pressure

If the vapour pressure in your grow space is too high, it can lead to excessive transpiration. This causes your plants to lose more water than they can absorb. This can result in dehydrated plants, wilted leaves, and even nutrient imbalances.

On the other hand, if the vapour pressure is too low, your plants may struggle to transpire effectively. This can lead to reduced nutrient uptake and stunted growth.

Benefits of achieving the right balance

Now, imagine your plants surrounded by the perfect vapour pressure conditions. They’ll flourish, soak up nutrients like sponges, and display vibrant, healthy growth. By maintaining optimal vapour pressure levels, you’ll maximise your plants’ potential and improve yields. You’ll create a haven where your plants can thrive and produce top-notch buds!

How do you calculate vapour pressure?

Alright, it’s time to unveil your secret weapon for achieving precision control over your grow environment—the vapor pressure calculator! This invaluable tool will take the guesswork out of maintaining the perfect vapour pressure levels for your cannabis plants. So, grab your notebooks and let’s dive into the world of accurate calculations!

Introducing the vapour pressure calculator and its purpose

The vapour pressure calculator is a handy online tool designed to help you determine the vapour pressure in your grow space. It takes into account factors such as temperature, humidity, altitude, and air circulation to provide you with precise measurements. With this vapour pressure calculator at your fingertips, you’ll be able to fine-tune your grow environment like a seasoned pro.

Step-by-step guide on using the calculator

Now, let’s walk through the process of using the vapour pressure calculator step by step. Follow these simple instructions, and you’ll be on your way to achieving vapour pressure perfection:

Gathering the necessary data

To get accurate results, you’ll need to collect a few essential pieces of data, such as temperature and humidity readings. There are many different methods of data collection that you could use. By far the most convenient and accurate way is to use a grow room sensor.

A Grow Sensor is a device that you place inside your grow room to measure and provide feedback on your environment. It collects data on various factors such as temperature, humidity, CO2 concentration, light spectrum, airflow, etc. By analysing this data, you can make improvements to optimise your grow space. You can configure the grow room sensors to send alerts and enable remote monitoring, saving time and reducing labour costs.

The Grow Sensor empowers you to monitor your grow spaces and access actionable insights. This valuable information allows you to enhance the quality, quantity, and consistency of your plants.

With the Grow Sensor, you can effectively identify and manage microclimates, solve problems, and minimise nutrient waste and pest issues. The innovative hardware and precise wireless sensor equipment are designed for easy installation. They also provide reliable connectivity, and unbeatable accuracy to support your growth endeavours.

Entering the data into the calculator

Find a reputable vapour pressure calculator online and input your gathered data. Typically, the calculator will prompt you to enter the temperature, humidity, altitude, and any other specific parameters it requires. Follow the instructions carefully and double-check your inputs for accuracy.

Interpreting the results

Once you’ve entered all the necessary data, the vapour pressure calculator will work its magic. The calculator will provide you with the vapour pressure measurement in your grow space. Take note of the values and pay attention to any additional insights or recommendations provided by the calculator. This information will be instrumental in fine-tuning your growing conditions.

The Grow Sensor hanging in front of the Grow app on The iPhone

Highlighting the benefits of using a vapour pressure calculator

Now you know how to use the vapour pressure calculator. Let’s explore the benefits it brings to your cannabis cultivation journey:

Accurate control over the growing environment:

The calculator eliminates guesswork and provides you with precise vapour pressure measurements. This allows you to fine-tune temperature and humidity levels, ensuring your plants receive the optimal conditions for healthy growth.

Enhanced plant health and growth:

By maintaining the ideal vapour pressure levels, your cannabis plants will thrive. They’ll absorb nutrients more efficiently, experience reduced stress, and exhibit vigorous growth, resulting in bountiful harvests of high-quality buds. The data provided by the calculator will help you tailor your grow room specifically for each stage of growth.

So, it’s time to harness the power of the vapour pressure calculator and elevate your cannabis cultivation game!

Factors affecting vapour pressure calculation

Now you have a good grasp of the vapour pressure calculator and its benefits.  It’s time to explore the various factors that can influence vapour pressure calculations. Understanding these factors will allow you to make informed adjustments and fine-tune your grow environment for optimal conditions. So, let’s dive into the key variables at play!

Temperature: The primary influencer

Temperature takes centre stage when managing vapor pressure. As the temperature rises, so does the vapour pressure. This means that higher temperatures lead to increased evaporation and higher humidity levels. On the other hand, lower temperatures result in lower vapour pressure and decreased evaporation.

To create the ideal environment for your cannabis plants, it’s crucial to maintain the right temperature range. A temperature between 20°C and 28°C (68°F and 82°F) during the vegetative stage is ideal. Slightly lower temperatures (in the suggested range) during the flowering stage are ideal.

Humidity: A crucial parameter

Humidity plays a significant role in determining vapour pressure. The higher the humidity, the higher the vapour pressure, as more water molecules are present in the air. Conversely, lower humidity leads to lower vapour pressure.

Different growth stages of cannabis have varying humidity requirements. During the vegetative stage, aim for a relative humidity (RH) level of around 50-70%. This range provides ample moisture for robust growth without promoting excessive moisture-related issues.

As your plants transition into the flowering stage, gradually decrease the humidity to around 40-50%. This will help to prevent the onset of mould and mildew.

Altitude: An often overlooked factor

Altitude, or the elevation above sea level, can also impact vapour pressure calculations. As you climb higher, the air pressure decreases, affecting the boiling point and subsequently altering vapour pressure. At higher altitudes, the boiling point of water is lower, resulting in lower vapour pressure.

If you’re cultivating cannabis at higher altitudes, it’s important to take this factor into account when using the vapour pressure calculator. Adjustments may be necessary to ensure accurate readings and to maintain the ideal vapour pressure range for your plants.

Troubleshooting vapour pressure issues

Picture showing how vapour pressure deficit affects the plants you grow

As much as we strive for perfection in our cannabis cultivation journey, sometimes challenges arise. But fear not! In this section, we’ll explore common vapour pressure issues and provide you with practical solutions to overcome them. So, let’s roll up our sleeves and tackle these challenges head-on!

Identifying signs of high or low vapour pressure

Before we dive into the solutions, it’s crucial to recognise the indications that your grow space is experiencing vapour pressure stress. Keep an eye out for the following indicators:

Signs of high vapour pressure:

  • Excessive condensation on surfaces
  • Wilted or droopy leaves
  • Mold or mildew growth
  • Reduced nutrient absorption and nutrient deficiencies

Signs of low vapour pressure:

  • Slow plant growth and stunted development
  • Dry, crispy leaves
  • Increased nutrient accumulation and nutrient toxicity
  • Lack of transpiration or reduced water uptake

Solutions for high vapour pressure

If you’re facing high vapour pressure in your grow space, don’t panic! There are practical steps you can take to bring it back into balance:

Adjusting temperature and relative humidity levels:

  • Increase ventilation and airflow to reduce humidity levels.
  • Utilise dehumidifiers or air conditioning units to control excessive moisture.
  • Fine-tune temperature settings to maintain the optimal range for your plants.

Improving ventilation and air circulation:

  • Install fans to improve air movement and prevent stagnant pockets of high humidity.
  • Position fans strategically to ensure proper airflow throughout the grow space.
  • Consider using oscillating fans to distribute air more effectively.

Solutions for low vapour pressure

On the flip side, if your vapour pressure is too low, don’t worry—we’ve got you covered! Here are some remedies to help you increase vapour pressure in your grow space:

Increasing temperature and humidity:

  • Adjust your heating system to maintain a slightly higher temperature range.
  • Use humidifiers or evaporative coolers to introduce moisture into the air.
  • Consider misting or foliar spraying your plants to provide additional humidity.

Using supplemental humidification methods:

  • Employ a humidifier specifically designed for grow environments to increase humidity levels.
  • Safely place trays of water near heat sources to enhance evaporation and raise humidity.
  • Utilise humidification systems that provide a controlled and consistent release of moisture.

By implementing these solutions, you’ll be able to fine-tune the vapour pressure in your grow space. This ensures that your cannabis plants receive the optimal conditions for healthy growth.


You’ve now journeyed through the intricate world of vapour pressure calculation. You’ve gained valuable insights into its significance for successful cannabis growing. Armed with the knowledge and troubleshooting advice, you’re well-equipped to create the optimal environment for your precious plants.

Remember, maintaining the ideal vapour pressure requires attention to detail, precision, and a deep understanding of your plants’ needs. By utilising the vapour pressure calculator, you can effortlessly navigate the complexities of temperature, humidity, and altitude. This will help to ensure your cannabis garden thrives in an environment perfectly tailored to its requirements.

As you continue on your cannabis cultivation journey, keep a keen eye on the signs of high or low vapour pressure. If you spot signs, address them promptly. By making adjustments, such as controlling temperature and humidity levels you’ll be able to maintain that sweet spot of vapour pressure. Improving ventilation and humidification methods will also help.

Always remember that the key to success lies in observation and adaptation. Observe your plants closely, listen to what they’re telling you through their growth patterns and health.  Adapt your cultivation practices accordingly. With time, patience, and a touch of passion, you’ll witness your indoor grow flourish.

Happy growing! May your cannabis garden be filled with lush green leaves, vibrant buds, and a harvest that surpasses your wildest dreams!

Share this post
Lucy Starley
November 16, 2023
8 min read

Get your free VPD & environment calculator

Perfect your environment.
Stay in the VPD sweet spot.
Ideal temperature ranges for day & night.
Prevent mould.
Induce colour.
Grow the best plants.
We care about your data in our privacy policy.
Your download will land in your inbox shortly.
Oops! Something went wrong while submitting the form.
Screenshot of our FREE VPD chart and environmental calender
Monitor your grow rooms with the Grow Sensor. Access grow room data anywhere, anytime.
We care about your data in our privacy policy.
😉 You have been added to the waiting list.
Oops! Something went wrong while submitting the form.
The Grow Sensor hanging in front of an iPhone displaying an overview of all grows within the Grow AppArrow
Get your FREE impartial list of the best grow room sensors now. Buy the right sensor for your grow room environment.
Sort by price.
Compare features like CO2 & VPD.
Includes affordable & premium sensors.
Check availability in your location.
Make an informed decision.
We care about your data in our privacy policy.
😉 It's on the way to your inbox.
Oops! Something went wrong while submitting the form.
The grow sensor hanging from its cable.
Grow the best plants with your FREE CO2 calculator.
We care about your data in our privacy policy.
😉 It's on the way to your inbox.
Oops! Something went wrong while submitting the form.
The grow room CO2 calculator.
Our blog

Latest blog posts

Get the latest grow news, tips and tricks here.
A grower measuring the leaf surface temperature of a cannabis plant using an Infrared thermometer.
Indoor growing

Why is leaf surface temperature important?

Learn why leaf surface temperature is key to healthy plant growth.
User avatar
Drew Cano
11 Jan 2022
5 min read
A healthy cannabis seedling under the correct PPFD.

What’s the best PPFD for seedlings? The cannabis edition

Optimize PPFD levels for your cannabis seedlings to maximise growth.
User avatar
Drew Cano
11 Jan 2022
5 min read
A man checks the temperature of his grow room.
Indoor growing

What happens if your grow room is too hot?

High Temperatures' Impact on Indoor Plant Growth.
User avatar
Drew Cano
11 Jan 2022
5 min read
An IR heat gun measuring the temperature of a cannabis leaf.
Indoor growing

Where do you measure temperature in a grow room?

Essential tips for measuring grow room temperature
User avatar
Drew Cano
11 Jan 2022
5 min read
Young plants under a grow light in an indoor grow room.
Indoor growing

What's the difference between PPFD and daily light integral?‍

Learn the difference between PPFD and DLI and how it effects indoor plant growth.
User avatar
Drew Cano
11 Jan 2022
5 min read
A close up of A CO2 regulator.
Indoor growing

Does CO2 speed up flowering?

Exploring CO2's role in speeding up plant flowering, especially cannabis.
User avatar
Drew Cano
11 Jan 2022
5 min read
A grower checks his plants in an indoor grow room.
Indoor growing

Save electricity costs using DLI

Cut indoor growing costs with DLI optimisation.
User avatar
Drew Cano
11 Jan 2022
5 min read
Some young plants under a led grow light.
Indoor growing

Why is daily light integral important?

Find out why daily light integral (DLI) is the key for an optimal harvest.
User avatar
Drew Cano
11 Jan 2022
5 min read