Ksp from solubility calculator
Turn a molar solubility into a solubility product: a 1:1 salt such as silver chloride that dissolves to 0.01 mol/L has a Ksp of 0.0001, while calcium fluoride at the same solubility gives 4 × 10⁻⁶. Free in your browser.
- Free
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- No sign-up
- Your data stays on your device
Run — free
Worked example
- Solubility
- 0.01
- Stoichiometry
- 1, 1
- Ion concentrations
- 0.01, 0.01
- Ksp
- 0.0001
- Exponent
- 2
- Prefactor
- 1
This Ksp from solubility calculator turns a measured or textbook molar solubility into the solubility product for a sparingly soluble salt. Enter the molar solubility s in moles per liter of formula units and the positive dissociation stoichiometry coefficients for each ion released per formula unit — for example one and one for silver chloride, one and two for calcium fluoride, or two and one for silver sulfate — and the engine returns Ksp as the product over i of (ν_i times s) raised to ν_i, together with the individual ion concentrations, the closed-form prefactor and total exponent, and a short formula reminder. The path is fully deterministic: finite arithmetic only, no network calls, no sampling, and no date-dependent shortcuts. Classic checks include s equals 0.01 with stoichiometry one-one giving Ksp equals 1e-4, and s equals 0.01 with one-two giving Ksp equals 4e-6. Negative solubility is rejected rather than silently producing a nonsense constant.
What Ksp from molar solubility tells you
The solubility product Ksp is the equilibrium constant for the dissolution of a sparingly soluble ionic solid when pure solid is present and activities of pure solids are taken as one. For a salt that fully dissociates into ions with stoichiometric coefficients ν_i per formula unit, each ion concentration at saturation equals ν_i times the molar solubility s of the formula unit. Substituting those concentrations into the equilibrium expression yields Ksp equals the product over i of (ν_i times s) raised to the power ν_i.
That identity is equivalent to a constant prefactor times s raised to the sum of the ν_i: for a one-to-one salt the prefactor is one and the exponent is two, for calcium fluoride the prefactor is four and the exponent is three, and for an A two B three salt the prefactor is one hundred eight and the exponent is five.
Where Ksp from solubility fits in study, lab work, and software
Students meet this conversion when a textbook gives the molar solubility of a sparingly soluble salt and asks for Ksp, when a lab measures how many moles of solid dissolve per liter of pure water, or when a contest problem supplies s and the dissociation pattern without walking through an ICE table. Teachers can pre-generate answer keys for modest solubility sets without trusting opaque calculator apps that silently drop the stoichiometric prefactor of four for AB two salts or forget the twenty-seven for AB three solids.
Developers call the same contract from scripts to seed deterministic test vectors for precipitation solvers, to normalize user-entered solubility and ion counts before equilibrium demos, or to satisfy programming-challenge statements that demand Ksp rather than a hand-waved s squared guess. Process and education tools use the evaluation when a learner types s and ν and the UI must show ion concentrations, the prefactor, the total exponent, and the numeric Ksp for step-by-step checking against the closed form.
What you can do with it
Homework and solubility-product checks
Convert textbook molar solubilities and AB, AB₂, or A₂B₃ stoichiometry into Ksp for worksheets and exam prep.
Lab and tutoring software
Normalize measured molar solubility and dissociation pattern into Ksp for lab notebooks, plotters, and interactive lessons.
FAQ
What does the Ksp from solubility calculator cost?
It is free in your browser on this page.
How is Ksp defined here?
Ksp = ∏_i (ν_i · s)^{ν_i} where s is the molar solubility of the formula unit and ν_i are the positive ion coefficients per formula unit. Equivalently Ksp = (∏ ν_i^{ν_i}) · s^{Σ ν_i}.
What happens if solubility is negative?
Molar solubility cannot be negative when computing the solubility product from s.
How do I enter CaF₂ or Ag₂SO₄?
Use stoichiometry [1, 2] for CaF₂ (one Ca²⁺ and two F⁻) and [2, 1] for Ag₂SO₄ (two Ag⁺ and one SO₄²⁻). Both give the closed form 4 s³.
Does this tool solve for solubility from a known Ksp?
No. It only evaluates Ksp from known molar solubility and stoichiometry. Use a dedicated inverse or root-finding tool if you need s from Ksp.
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/chem/ksp-from-solubility \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"solubility":0.01,"stoichiometry":[1,1]}'const res = await fetch("https://api.kit.forhosting.com/chem/ksp-from-solubility", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"solubility": 0.01,
"stoichiometry": [
1,
1
]
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/ksp-from-solubility",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"solubility": 0.01,
"stoichiometry": [
1,
1
]
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/ksp-from-solubility", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"solubility":0.01,"stoichiometry":[1,1]}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"solubility":0.01,"stoichiometry":[1,1]}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/ksp-from-solubility", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"solubility": 0.01,
"stoichiometry": [
1,
1
]
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.ksp_from_solubility",
"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_abs_value | 1000000000000000 |
max_ions | 12 |
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
What Ksp from molar solubility means and what the response contains
This calculator returns the normalized solubility, the stoichiometry array, the list of ion concentrations at saturation, the numeric ksp, the summed exponent, the multiplicative prefactor, the method tag ksp_from_solubility, the precision used, a compact formula string, and a unit note that Ksp carries concentration units raised to the total ion count when s is in mol per liter. There is no approximate CAS path and no Monte Carlo sampling of solubilities: the engine either builds a finite floating-point Ksp inside the supported ranges or rejects the input with invalid_input. Rejected cases include missing fields, non-finite values, empty or non-positive stoichiometry entries, more than twelve ion coefficients, magnitudes above the documented ceiling, and any negative molar solubility, because a physical saturated solution cannot have a negative formula-unit concentration.
How solubility and stoichiometry are read and kept reproducible
Stoichiometry must be a non-empty array of finite positive numbers in formula-unit order; typical textbook pairs are one-one for silver chloride style salts, one-two for AB two salts such as calcium fluoride, two-one for A two B salts such as silver sulfate, and two-three for A two B three solids. Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces, hex prefixes, and non-numeric tokens are rejected with a clear message so a bad cell does not become a wrong Ksp. Zero solubility is valid and yields Ksp equal to zero, which is the finite limit when no solid dissolves. The preferred fields are solubility for the molar solubility s in mol per liter and stoichiometry for the parallel list of positive ion coefficients, but aliases s, molar_solubility, S, and sol for the first, and coeffs, coefficients, nu, ions, stoich, and ion_coefficients for the second, are accepted so spreadsheets, query strings, and typed forms can reuse the same contract. A negative solubility fails with invalid_input because the saturated concentration cannot be negative and raising negative concentrations to non-integer powers would be ill-defined for many salts. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for large values and how many significant digits to preserve for tiny Ksp results, defaulting to ten and capped at fifteen so JSON goldens stay stable without collapsing real microscopic products to zero. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing the Ksp product yourself.
Where Ksp from solubility fits in study, lab work, and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result. Pair it with total-ion-concentration helpers when you need ionic strength estimates, with freezing-point or boiling-point tools when colligative properties follow from dissolved ions, and with other chemistry endpoints when you are assembling a small lab of free, deterministic solubility and equilibrium helpers.
Integration use cases
Deterministic test fixtures
Generate reproducible ksp, prefactor, and ion_concentrations fields for unit tests, property checks, and CI assertions.