💧 Watering Calculator
Enter your pot size, GPH (gallons per hour) of your drip emitters, number of emitters per pot, and your VWC (Volumetric Water Content) targets. The calculator determines how much water each shot should deliver and how long to run your pumps.
Key inputs:
• WHC % — Water Holding Capacity of your substrate (coco ~55-65%, rockwool ~70-80%, peat ~60-70%)
• Start VWC % — Current moisture level in your pots
• Target VWC % — Where you want moisture to be after watering (cannot exceed WHC)
• Runoff % — Extra water beyond what the pot holds (typically 10-20%)
The schedule shows exact start times and duration for each shot throughout the day.
📋 Quick Calc
Pick your growth stage and substrate — the tool auto-fills VWC targets and dryback percentages from crop steering presets, then generates a watering plan instantly.
☀️ DLI/VPD
• DLI (Daily Light Integral) — Total light delivered per day. Formula: PPFD × hours × 3600 ÷ 1,000,000. Target: 35-45 mol/m²/day in flower.
• VPD (Vapor Pressure Deficit) — The difference between water vapor pressure at saturation and actual. Target: 1.0-1.4 kPa in flower. Too low = slow transpiration, too high = plant stress.
Select a stage card to see if your DLI and VPD are in the optimal range.
🧪 Nutrients
Select a nutrient brand, product line, growth stage, and gallons of water. The calculator shows exactly how many mL or grams of each product to add. Covers 9 brands: General Hydroponics, Advanced Nutrients, Athena, FoxFarm, Botanicare, Drip Hydro, Mills, House & Garden, and Canna.
EC targets are shown per stage — these are the electrical conductivity goals for your nutrient solution. Higher EC = more nutrients in the substrate.
Always mix products one at a time, fully dissolving each before adding the next. Check pH after mixing.
📊 Crop Steering Presets
Reference table showing VWC targets, dryback percentages, EC ranges, and environmental conditions (VPD, temp, RH) for each growth phase. Use these as guidelines — adjust based on your specific genetics and environment.
🌱 Growing Advice
Pre-computed crop steering recommendations based on your stage and substrate. Includes watering strategy, EC guidance, environmental targets, and warnings. No AI needed — this is the same logic from the ARC Labs platform.
📤 Share & 🖨️ Print
Share generates a URL with all your calculator inputs — send it to anyone and they'll see your exact plan. Print opens a clean printable schedule you can tape to the wall.
📱 Install
Add this calculator to your phone's home screen for quick access — works offline once installed. No app store needed.
Questions? Email info@arclabcanna.com — Free tool by ARC Labs
