Cannabis Yield Estimator
Estimate your potential dry weight harvest based on lighting and grow environment.
Estimated Dry Yield
How to Estimate Cannabis Yields
Predicting the final harvest weight of a cannabis grow is more science than guesswork. While genetics play a massive role, the primary limiting factor for indoor cultivation is usually lighting intensity and efficiency. This calculator uses the "Grams Per Watt" (GPW) benchmark, which is the industry standard for estimating yields.
Understanding Grams Per Watt (GPW)
The GPW metric measures the efficiency of your grow. It calculates how many grams of dried, cured flower you produce for every watt of electricity your grow lights consume.
- 0.5 GPW: Typical for beginners or growers using older HPS/MH lighting without optimized environments.
- 1.0 GPW: The "Golden Standard" for HPS growers and a baseline for decent LED growers.
- 1.5 – 2.5+ GPW: Achievable with high-efficiency modern LEDs, perfect Vapor Pressure Deficit (VPD), CO2 enrichment, and expert nutrient management.
Key Factors Affecting Your Harvest
To maximize the numbers shown in the calculator above, focus on these variables:
1. Lighting Spectrum and Intensity
Not all watts are created equal. A 600W LED bar light produces significantly more Photosynthetically Active Radiation (PAR) than a 600W HPS bulb. Full-spectrum LEDs generally produce denser buds and higher resin content.
2. Grow Space Environment
Temperature and humidity control are critical. If your plants are stressed by heat or lack of airflow, they will stunt, drastically reducing yield regardless of your light power.
3. Training Techniques
Techniques like Low Stress Training (LST), Topping, and Screen of Green (SCROG) ensure the light hits more bud sites. A flat canopy allows all buds to receive equal light intensity, increasing the overall weight of the harvest.
4. Genetics
Yield potential is encoded in the seed. Some strains are "heavy yielders" bred for commercial production (like Big Bud or Critical Mass), while others are lower-yielding boutique strains prized for flavor rather than weight.