Water-soluble fertilizer calculator
Turns a ppm target into grams on the scale: 200 ppm nitrogen in 10 litres with a 20% bag needs 10 grams of product. Built for greenhouse tanks, hydroponic batches and watering cans. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Volume
- 10
- Concentration
- 200
- Fertilizer strength
- 20
- Volume unit
- L
- Concentration unit
- ppm
- Fertilizer strength unit
- percent
- Fertilizer g
- 10
Mixing a water-soluble fertilizer is a tank problem, not a lawn-area problem. You already know the volume of solution you want, the target nutrient concentration in parts per million, and the fertilizer strength printed as a percent on the bag analysis. This water-soluble fertilizer calculator converts those three numbers into grams of product to dissolve, using the standard greenhouse identity fertilizer grams equals concentration times volume divided by strength times ten.
How grams of water-soluble fertilizer are computed from ppm, volume, and bag strength
A water-soluble fertilizer mix starts from the identity that one part per million of a nutrient is one milligram of that nutrient in one litre of solution. Multiply the target concentration in ppm by the tank volume in litres and you have the milligrams of nutrient the tank must hold. Divide the required nutrient milligrams by that fraction and convert milligrams to grams.
Algebraically the steps collapse to fertilizer grams equals concentration times volume divided by fertilizer strength times ten. Check: two hundred ppm nitrogen in ten litres with a twenty percent bag needs two thousand milligrams of nitrogen, which is ten grams of product, matching two hundred times ten divided by twenty times ten. Another check: one hundred fifty ppm in fifty litres at fifteen percent strength is fifty grams of product.
The response also reports fertilizer grams per litre so you can scale a stock recipe, the water volume in litres as the tank fill, and the nutrient milligrams for a lab or conductivity log. The pipeline is deterministic floating-point arithmetic with no random seeds, no wall-clock timestamps, and no network. Concentration and volume may be zero, meaning a tank with no nutrient or an empty tank, and then fertilizer grams is zero.
Where a water-soluble fertilizer calculator earns its keep
Greenhouse growers and hydroponic operators use a water-soluble fertilizer calculator so a stock tank or a drip batch matches a published ppm program instead of a tablespoon guess. A nursery mixing a 20-20-20 feed at two hundred ppm nitrogen in a ten-litre jug needs ten grams on the scale, not a lawn-bag chart written in pounds per thousand square feet. Fertigation technicians convert a house ppm target and a known injector tank volume into a weigh-out they can pin in a standard operating procedure.
Teaching labs and extension short courses need a deterministic oracle that uses the same divide-by-ten metric identity printed on greenhouse worksheets, so a classroom example and a production script never disagree. Gardeners dissolving a soluble houseplant feed into a watering can use the same contract: volume of water, target ppm from the label or a grower sheet, and the first N-P-K number as fertilizer strength.
This page is not a lawn fertilizer calculator: that search asks how many pounds of bagged product to buy from turf area, a nitrogen rate per thousand square feet, and bag N percent. It is also not a laboratory molarity or weight-volume percent prep: those searches ask for moles or percent w/v without a fertilizer analysis. Failed validation does not consume balance.
What you can do with it
Greenhouse stock-tank weigh-out
Enter tank litres, the house ppm target, and the bag nutrient percent to read grams of water-soluble fertilizer and the water fill for that batch.
Hydroponic reservoir recipe
Convert a reservoir volume and a nutrient ppm program into fertilizer grams per litre so the same recipe scales from a trial bucket to a production tank.
FAQ
What is fertilizer strength on a water-soluble bag?
Fertilizer strength is the guaranteed analysis percent of the nutrient you are targeting. Use 20 for a 20-20-20 nitrogen program, or the matching P or K number if that is the nutrient in the ppm target.
Why was my concentration or volume rejected?
Zero is allowed and returns zero grams. Strength must be greater than zero and at most 100.
How is this different from a lawn fertilizer calculator?
A lawn fertilizer calculator converts turf area and pounds of nitrogen per thousand square feet into pounds of bagged product. This page mixes a tank: ppm, litres, and bag percent into grams of water-soluble fertilizer.
How many grams of fertilizer do I need for 200 ppm in 10 litres?
With a 20% nitrogen bag you need 10 grams. The tank must hold 2000 milligrams of nitrogen, and because only a fifth of the product is nitrogen, that takes 10 grams of fertilizer.
What is the formula for fertilizer grams from ppm?
Multiply the target ppm by the volume in litres, then divide by the bag percent times 10. For 150 ppm in 50 litres with a 15% product, the result is 50 grams.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/bio/water-soluble-fertilizer \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"volume":10,"concentration":200,"fertilizer_strength":20}'const res = await fetch("https://api.kit.forhosting.com/bio/water-soluble-fertilizer", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"volume": 10,
"concentration": 200,
"fertilizer_strength": 20
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/bio/water-soluble-fertilizer",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"volume": 10,
"concentration": 200,
"fertilizer_strength": 20
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/bio/water-soluble-fertilizer", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"volume":10,"concentration":200,"fertilizer_strength":20}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"volume":10,"concentration":200,"fertilizer_strength":20}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/bio/water-soluble-fertilizer", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"volume": 10,
"concentration": 200,
"fertilizer_strength": 20
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "bio.water_soluble_fertilizer",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_volume | 1000000 |
max_concentration | 1000000 |
max_strength | 100 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Negative concentration or volume is rejected with invalid_input instead of producing a negative bag weight.
How grams of water-soluble fertilizer are computed from ppm, volume, and bag strength
The bag is not pure nutrient: fertilizer_strength is the guaranteed analysis percent of the nutrient you are targeting, so twenty on a 20-20-20 label means twenty percent nitrogen by mass. Either quantity below zero is invalid_input, because a negative tank or a negative ppm has no physical mixing interpretation and must not become a silent negative weigh-out.
Input contract, response shape, and error behaviour
Negative volume or negative concentration is rejected with a message that the quantity cannot be negative. Fertilizer strength must be strictly greater than zero and at most one hundred; a zero analysis would divide by zero, and a percent above one hundred is not a bag guarantee. Values above the declared ceilings of one million litres or one million ppm are also rejected. POST a JSON body with three required finite numbers: volume for the finished solution in litres, concentration for the target nutrient level in ppm, and fertilizer_strength for the bag percent of that nutrient. Each field may arrive as a JSON number or as a numeric string; aliases volume_l, liters, litres, target_ppm, ppm, target_concentration, strength, nutrient_percent, and analysis_percent are accepted. Missing required fields, non-numeric strings, NaN, and Infinity fail with invalid_input naming the field and are not billed. On success the body echoes the cleaned inputs, sets volume_unit to L, concentration_unit to ppm, and fertilizer_strength_unit to percent, and returns fertilizer_g as the product mass to weigh, water_l as the tank fill, and nutrient_mg as the milligrams of nutrient in the batch. When volume is positive the body also includes fertilizer_g_per_l and nutrient_mg_per_l; those per-litre fields are omitted when the tank is empty so optional keys never appear as null. A formula string and a formula_applied line restating the arithmetic travel with every success so a notebook can print the identity next to the weigh-out. Example: volume ten, concentration two hundred, fertilizer_strength twenty yields ten grams of fertilizer and ten litres of water. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where a water-soluble fertilizer calculator earns its keep
Pin fertilizer_g and water_l in tests, keep inputs inside the declared ceilings, and you get the same ten grams for two hundred ppm in ten litres at twenty percent strength in a lecture notebook, an LMS plugin, and a fertigation script.
Integration use cases
Classroom and SOP check
Pin fertilizer_g against the greenhouse identity (ppm × litres) / (strength × 10) so a worksheet, a widget demo, and a fertigation script stay aligned.
Technical questions
How do I calculate grams of water-soluble fertilizer for a target ppm?
Send volume in litres, concentration in ppm, and fertilizer_strength as the bag percent of the target nutrient. The API returns fertilizer_g = (concentration × volume) / (fertilizer_strength × 10).
What does the water-soluble fertilizer calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.