Fertigation PPM Calculator
Stock strength and ratio to applied ppm and mix.
What it does
Fertigation feeds through drip lines at parts-per-million precision, but stock buckets mix by ounces per gallon. The bridge is injector ratio: stock ppm divided by water parts. Three inputs land the dose.
The tool above converts stock strength to ppm, divides by injector ratio for applied ppm, and totals fertilizer per tank. Imperial mode speaks ounces and gallons; metric mode speaks grams and liters with matching results.
Extension greenhouse guides teach this stock-and-ratio method with EC verification at emitters. Injector ratios near 100 or 200 to 1 dominate, and crop targets cluster near 100 to 200 ppm nitrogen for most crops.
Mix to the math, then trust the meter. Empty stock tanks, stuck injectors, and clogged filters all read fine on paper while lines run clear. Weekly EC checks catch every silent failure.
How to use
- Pick imperial (oz, gal, lb) or metric (g, L, kg).
- Enter fertilizer N percent.
- Enter stock strength and injector ratio.
- Enter tank size.
- Read applied ppm, stock ppm, and fertilizer.
- Verify EC at the emitter.
Formula
- N%
- Fertilizer nitrogen percent.
- stock
- Stock mix strength in oz/gal (g/L metric).
- ratio
- Water parts per stock part.
Fertilizer per tank prorates stock concentration by tank size (oz/gal times gallons over 16 for lb, g/L times liters over 1000 for kg). EC verification at the emitter closes the loop.
Worked example
Example: 125 ppm N lines
16 oz/gal stock of 20 % N at 200:1 into 100 gal.
- Stock is 16 oz/gal of 20 % N: 16 x 20 x 78.125 = 25,000 ppm.
- Injector runs 200 to 1.
- Applied: 25000 / 200 = 125 ppm N.
- 100 gal tank needs 16 x 100 / 16 = 100 lb.
- Check EC at the emitter after mixing.
Reference table
| Stock | N% | Applied |
|---|---|---|
| 5 oz/gal | 20 % | 78 ppm |
| 10 oz/gal | 20 % | 156 ppm |
| 16 oz/gal | 20 % | 125 ppm at 200:1 |
| 100 g/L | 20 % | 200 ppm |
| 125 g/L | 20 % | 125 ppm at 200:1 |
Limits
- Nitrogen math only. Other nutrients ride along unchecked.
- Assumes calibrated injector ratios.
- Mix compatibility needs jar tests.
- Crop targets vary by stage.
Common mistakes
- Confusing stock ppm with applied ppm.
- Skipping EC verification.
- Mixing incompatible chemicals.
- Running empty stock tanks.
- Forgetting ratio changes with injectors.
Try it yourself
Quick checks. Answers sit tucked under each question.
15 % N at 10 oz/gal, 100:1, 50 gal tank?
Stock is 10 x 15 x 78.125 = 11,719 ppm. Applied is 11719 / 100 = 117.2 ppm. Fertilizer is 10 x 50 / 16 = 31.3 lb.
15 % N at 100 g/L, 100:1, 200 L tank?
Stock is 100 x 15 x 10 = 15,000 ppm. Applied is 15000 / 100 = 150 ppm. Fertilizer is 100 x 200 / 1000 = 20 kg.
Questions
How is applied ppm figured?
Stock ppm equals oz/gal times N percent times 78.125 (imperial) or g/L times N percent times 10 (metric). Applied ppm divides stock by the injector ratio.
What injector ratios are common?
1 to 100 and 1 to 200 most often, fixed by the injector model. Ratio means parts water per part stock; higher ratios dilute further.
What ppm should lines carry?
100 to 200 ppm N for most greenhouse crops, lower for seedlings, higher for heavy feeders. Crop guides set targets; this page hits them.
Does metric work the same?
Yes: 125 g/L of 20 % N makes 25,000 ppm stock, and 200:1 gives 125 ppm applied with 50 kg per 400 L tank. Units convert, chemistry does not care.
Why did ppm crash mid-week?
Stuck check valves, empty stock tanks, and clogged filters silently pass clear water. EC checks at the emitter catch all three weekly.
Can I mix pesticide in the stock?
Acids and calcium clash into gypsum sludge, and some pesticides never ride fertilizer. Jar-test new mixes overnight before tanking them.