Knowing and calculating your yield not only allows you to track your progress as a grower and set personal benchmarks, it will allow you to better evaluate efficiencies, make adjustments to increase yield and compare your grow operation to others in the industry. To do that, though, everyone needs to be measuring their yield the same way. Here are some common, and not as common, yield formulas:
1 Grams of dried product/square foot of canopy:
The industry benchmark, this formula allows you to get the most basic measure of your yield. Your square footage is simply the length of your canopy coverage multiplied by its width. Divide your total dried product weight by the square footage, and you will get your yield per square foot.
Formula: Total dried product weight ÷ Square footage of canopy = Yield per square foot
The bigger the number, the better the yield. It’s not the most accurate measure, as it doesn’t account for cycles per year – someone could have a tremendous yield/sq. ft., but if they are only turning two cycles/year, they are likely not producing as much as someone with a lower yield/sq. ft. who turns six cycles/year. Still, it is the most commonly used measure to compare crop yields. (72% of research participants indicated that they measure yield per square foot.)
2 Grams of dried product/cubic foot of canopy:
To calculate your canopy in cubic feet, simply multiply your square footage (from metric #1 above) by your canopy height. To calculate your yield, divide your total grams of dried product by your cubic footage.
Formula: Total dried product weight ÷ Cubic footage of canopy = Yield per cubic foot
This formula takes into consideration canopy height, which can greatly impact results compared to calculating yield with square footage only, especially if you are cultivating using vertical farming.
3 Grams of dried product/watt of light:
This formula allows you to calculate your yield relative to your total light power. To calculate, simply divide your dry weight by your lamp wattage.
Formula: Total dried product weight ÷ Total lamp wattage = Yield per watt of light
For example, if you’re using two 600W lamps (1200W total) and produced 1,020 grams of dry product, your calculation would be 1020g/1200W = 0.85g/W.
This formula allows you to measure your yield relative to your lamp strength, and can account for energy efficiency (or inefficiency) for different lighting sources. For example, if you’re using “energy efficient” LEDs that produce low yield, they are not actually efficient.
4 Grams of dried product/kilowatt-hour:
This is the industry standard measure that allows you to calculate your energy costs over your yield. To do this, you first need to calculate your daily energy usage: Multiply your total wattage by the number of light operating hours in a day.
Formula for total daily energy usage: Total light wattage x light operating hours per day = Total wattage hours
For example, if you’re using two 600W lamps on a daily, 12-hour cycle, your daily energy use will be 1200W x 12hours = 14,400 watt hours (Wh).
Divide that by 1,000 (since 1,000W equals 1kW) to get your kilowatt hours (kWh) per day.
Formula for kilowatt hours: Watt hours ÷ 1,000 = kWh
Then, multiply your kilowatt hours per day by the number of days your canopy has spent under lights.
Formula for kWh/cycle: kWh per day x number of days under lights = kWh/cycle
For example, using the above figures of 14,400Wh, or 14.4kWh, and if your cycle is 75 days, your formula would be: 14.4kWh x 75 days = 1080kWh used during your entire cycle.
Next, divide your yield in grams by your total kWh.
Formula for yield/kWh: Total dried product weight ÷ kWh/cycle = Yield per kWh
This measure will allow you to easily compare your yield relative to your energy costs, making it a useful tool to compare various lighting systems.