Free hydroponic calculators
Mix nutrient solution, convert EC and PPM, size your reservoir and cost your grow lights. Simple calculators for home hydroponic growers, with the formulas explained so you can check the maths.
Calculators
Setting up a reservoir: where to start
Whether you grow lettuce in a deep water culture tub or basil in an NFT channel, a new reservoir follows the same order. Each step has a calculator.
Step 1: Find your water volume
Every dose is per litre or per gallon, so start with the real amount of water in the tank. Use the reservoir volume calculator.
Step 2: Work out the nutrient dose
Enter the label dose of each part to get the millilitres to add to your reservoir. Use the hydroponic nutrient calculator.
Step 3: Check strength with a meter
Your meter confirms the mix. Convert readings to match a feeding chart written for another scale. Use the EC to PPM converter.
Step 4: Correct if you overshoot
Too strong or too weak? Find how much water or stronger solution to add. Use the hydroponic PPM calculator.
Guides for home growers
EC and PPM at a glance
PPM is calculated from EC, and meters use different factors, so the same water can show different ppm numbers. Reference values (EC × scale):
| EC (mS/cm) | 500 scale | 640 scale | 700 scale |
|---|---|---|---|
| 0.8 | 400 ppm | 512 ppm | 560 ppm |
| 1.0 | 500 ppm | 640 ppm | 700 ppm |
| 1.5 | 750 ppm | 960 ppm | 1,050 ppm |
| 2.0 | 1,000 ppm | 1,280 ppm | 1,400 ppm |
EC is the more reliable number to track. Check which scale your meter uses before following a ppm figure from a chart or forum post. Convert any value with the EC to PPM converter.
Why calculate instead of guessing
A reservoir is a small, closed system. A nutrient mix that is a little too strong can burn roots and leaf tips, and one that is too weak slows growth. Because the volume is small, a few extra millilitres is a big change in concentration. Measuring the water, scaling the dose to it and checking with a meter takes a couple of minutes and gives the same result every week.
Every calculator here shows its formula and a worked example, so you can see how the answer is reached and check it by hand.
Good habits for any system
- Calibrate your meters. EC and pH meters drift. Use calibration solution on the schedule the maker recommends.
- Mix parts separately. Add each nutrient part to water one at a time, stirring between, and never mix concentrates together.
- Top off with water, not full-strength nutrient. Plants drink water faster than nutrients, so ppm creeps up as the level drops.
- Change the reservoir on a schedule. Even if the readings look fine, the balance of nutrients shifts over time.
- Write readings down. A simple log of EC, pH and volume makes problems easy to spot.
Estimates only: always follow your nutrient manufacturer's label and check your readings with a calibrated meter.