The calculation can be described in four steps:
- Add volumes (ml) together to get overall volume
- Divide individual volumes by overall volume
- Multiply result to N, P, and K of each corresponding ratio
- Add Ns, Ps, and Ks
For example, let’s say you are combining two nutrients, 5 ml of 1-2-3 and 10 ml of 3-2-1. First, add their volumes:
| 5 ml + 10 ml = 15 ml |
Now that you have the combined volume, divide each volume by the overall volume (These example results have been rounded):
| 5 ml / 15 ml = 0.3 | 10 ml / 15 ml = 0.6 |
Next, multiply these results to their corresponding nutrient’s N-P-K ratio:
| Nutrient A (1 – 2 – 3) 0.3 [N] 1 x 0.3 = 0.3 [P] 2 x 0.3 = 0 .6 [K] 3 x 0.3 = 0.9 |
Nutrient B (3 – 2 – 1) 0.6 [N] 3 x 0.6 = 1.8 [P] 2 x 0.6 = 1.2 [K] 1 x 0.6 = 0.6 |
Now, add the Ns together, the Ps together, and the Ks together
| [N] 0.3 + 1.8 = 2.1 |
| [P] 0.6 + 1.2 = 1.6 |
| [K] 0.9 + 0.6 = 1.5 |
The combined N – P – K result is 2.1 – 1.6 – 1.5.
By correctly combining your ratios, you’ll be able to accurately determine what mixture satisfies the plant’s desired ratio. If you’d like to learn more about N – P – K ratios and how they apply to the different stages of cannabis growth, enroll in an Oaksterdam University course today!
Here is the same N – P – K combination example in a more condensed format which you can copy/paste for your own notes!
| Nutrient A – 5 ml (1 – 2 – 3) | Nutrient B – 10 ml (3 – 2 – 1) |
| 5 mL + 10 mL = 15 ml | |
| 5 mL / 15 mL = 0.3 [N] 1 x 0.3 = 0.3 [P] 2 x 0.3 = 0 .6 [K] 3 x 0.3 = 0.9 |
10 mL / 15 mL = 0.6 [N] 3 x 0.6 = 1.8 [P] 2 x 0.6 = 1.2 [K] 1 x 0.6 = 0.6 |
| [N] 0.3 + 1.8 = 2.1 [P] 0.6 + 1.2 = 1.6 [K] 0.9 + 0.6 = 1.5 |
|
| Overall NPK – 2.1, 1.8, 1.5 | |