Fertilizer Dilution Calculator
Get the math right. Kill fewer plants.
Your Fertilizer
Common fertilizers (click to fill):
Water Amount
Fertilizer Strength
✓ Safe for most houseplants
Add to your water:
1
tablespoon
per 1 gallon of water
Dilution ratio: 1:256
Resulting Nutrients
⚠️ Fertilizer Burn Risk
This dilution may be too concentrated for most houseplants. Consider using half strength or diluting further to avoid leaf burn and root damage.
🌿 Sensitive Plants Warning
This strength is too strong for ferns, orchids, and recently repotted plants. Use half strength or weaker on these plants.
ℹ️ Very Dilute
This dilution is very dilute and may not provide enough nutrients. Consider standard strength (1×) for actively growing plants.
❄️ Winter tip: Plants need less fertilizer during low-light months. Consider reducing to half strength or less.
Pro Tips
💧
Always water plants before fertilizing to prevent root burn.
📅
Feed actively growing plants every 2-4 weeks during spring/summer.
👀
Watch for brown leaf tips or yellowing — signs of over-fertilizing.
How to Use This Calculator
TL;DR: Enter your fertilizer's NPK ratio, how much water you're mixing, and the calculator tells you exactly how much fertilizer to use.
Step 1: Find Your NPK
Look at your fertilizer bottle. It has three numbers like "20-20-20" or "10-5-5". Enter those values in the NPK fields.
- N (Nitrogen): Promotes leaf growth and green color
- P (Phosphorus): Supports root development and flowering
- K (Potassium): Boosts overall health and disease resistance
Step 2: Choose Your Water Amount
Enter how much water you're mixing fertilizer into. Most people use 1 gallon for watering multiple plants, or 1 liter for a single plant.
Step 3: Set Fertilizer Strength
The slider defaults to 1× (standard strength). Adjust based on:
| Strength |
Best For |
| ⅛× to ½× |
Sensitive plants, winter feeding, seedlings |
| 1× (Standard) |
Most houseplants during growing season |
| 2× to 4× |
Heavy feeders, outdoor plants (use cautiously) |
Step 4: Calculate
Click "Calculate Dilution" and the calculator will tell you:
- Exactly how much fertilizer to add (in ml, teaspoons, or tablespoons)
- Resulting PPM (parts per million) for each nutrient
- Safety warnings if the concentration is too high
Why PPM Matters
PPM (parts per million) measures nutrient concentration. Most houseplants do best in the 100-200 ppm range for each nutrient.
| PPM Range |
What It Means |
| < 50 |
Very dilute — may not provide enough nutrients |
| 50-200 |
Ideal range for most houseplants |
| 200-400 |
Strong — fine for established plants |
| 400+ |
High concentration — risk of burn |
The golden rule: When in doubt, use less. Over-fertilizing is harder to fix than under-fertilizing.
Common Fertilizer Presets
| Preset |
NPK |
Best For |
| Jack's Classic 20-20-20 |
20-20-20 |
All-purpose for tropicals |
| Miracle-Gro All Purpose |
24-8-16 |
General feeding |
| Dyna-Gro Grow |
7-9-5 |
Foliage-focused, includes micronutrients |
| Espoma Indoor! |
2-2-2 |
Organic, gentle, slow-release |
| FoxFarm Grow Big |
6-4-4 |
Fast-growing tropicals |
| Bloom Booster |
10-30-20 |
Flowering plants |
Safety Notes
⚠️ Important:
- Start at half-strength if you're unsure — you can always increase
- Never fertilize dry soil — always water first to prevent root burn
- Flush soil monthly with plain water to prevent salt buildup
- Reduce or stop fertilizing in fall/winter when growth slows
- Watch for warning signs: brown tips, white crust on soil, wilting with wet soil
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