Pure mass from purity calculator
Find how much of a weighed sample is the substance you actually want: 25 g of material at 98.5 % purity holds 24.625 g of pure substance and 0.375 g of impurities, in the same unit you weighed. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Sample mass
- 25
- Purity percent
- 98.5
- Purity fraction
- 0.985
- Pure mass
- 24.625
- Impurity mass
- 0.375
Percent purity tells you how much of a weighed sample is actually the desired substance versus solvent, moisture, by-products, or filler. In preparative chemistry, quality control, and reagent prep, you often know the bottle mass and the assay percentage printed on the label, and you need the mass of pure analyte before converting to moles or planning a reaction scale. This calculator multiplies the impure sample mass by the purity fraction purity percent divided by one hundred, returns the pure mass in the same unit you supplied, and also reports the impurity mass so mass balance is visible at a glance. Purity must sit in the closed interval from zero to one hundred percent; values outside that range fail with a clear invalid input message instead of inventing a non-physical pure mass.
How pure mass is obtained from percent purity
Start from a weighed sample of mass m sample that is only partially pure. The certificate of analysis or reagent label quotes a mass-percent purity P, meaning that one hundred mass units of sample contain P mass units of the target substance. Convert the percentage to a dimensionless fraction by dividing by one hundred: f equals P divided by one hundred.
The pure substance mass is then the product m pure equals m sample times f, which is exactly m sample times P over one hundred. The complementary impurity mass is m impurity equals m sample minus m pure, so the two parts always sum back to the sample mass within floating-point rounding.
Boundary values are meaningful: P equals zero means none of the sample is the target substance and pure mass is zero; P equals one hundred means the sample is treated as fully pure and pure mass equals the sample mass. Values below zero or above one hundred are not valid percent purities for this definition and are rejected rather than clamped or wrapped. Sample mass must be finite and non-negative; NaN and Infinity are rejected.
Missing fields fail early with invalid input so clients can surface a field-level message before any charge is applied.
Where pure-mass-from-purity calculators show up in real work
Secondary-school and college general chemistry courses constantly assign percent-purity problems: a student weighs an impure sample, multiplies by the label purity, and then converts pure grams into moles for stoichiometry. Analytical and process labs read assay percentages from certificates of analysis and need a fast, shared conversion before feeding masses into dilution or reaction calculators. Purchasing and inventory teams estimate how much pure active ingredient they actually receive when a drum is quoted at ninety-nine percent rather than one hundred.
Quality-control scripts that ingest vendor COA tables can call this capability in bulk, reject out-of-range purity values automatically, and keep pure-mass columns consistent with hand-checked spreadsheets. If you later need moles from pure mass and molar mass, mass-fraction to mole-fraction conversion, or solution percent preparation, treat those as separate search intents and landings rather than overloading this pure-mass-from-purity calculator page.
What you can do with it
Homework purity-to-moles pipelines
Convert impure sample mass and label percent purity into pure mass before dividing by molar mass so stoichiometry answers match the textbook ground truth.
COA and reagent label checks
Turn certificate-of-analysis assay percentages and bottle weighings into pure active mass for batch records and inventory valuation.
FAQ
What purity range is allowed?
Purity percent must be between 0 and 100 inclusive.
What does it cost?
The browser tool is free and runs locally.
How do I get the pure mass from a percent purity?
Divide the purity by one hundred to get a fraction and multiply it by the sample mass. A sample of 10 g at 100 % purity, for instance, is 10 g of pure substance with no impurity at all.
What unit is the result in?
The same unit you used for the sample mass, whether grams, milligrams or kilograms. Pure mass and impurity mass always share that unit and add up to the sample mass.
How do I find the percent purity if I already know the pure mass?
That is the reverse question, answered by the percent purity calculator. This one starts from the sample mass and the purity on the label and gives you the pure mass.
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/mass-from-purity \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"sample_mass":25,"purity_percent":98.5}'const res = await fetch("https://api.kit.forhosting.com/chem/mass-from-purity", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"sample_mass": 25,
"purity_percent": 98.5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/mass-from-purity",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"sample_mass": 25,
"purity_percent": 98.5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/mass-from-purity", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"sample_mass":25,"purity_percent":98.5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"sample_mass":25,"purity_percent":98.5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/mass-from-purity", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"sample_mass": 25,
"purity_percent": 98.5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.mass_from_purity",
"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.
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
How pure mass is obtained from percent purity
The arithmetic is deterministic floating-point with no random seeds, wall-clock timestamps, network calls, or model drift, so identical inputs always produce identical JSON.
What you send and what you get back
Send two required fields. Classic textbook checks include twenty-five grams of material at ninety-eight point five percent purity giving about twenty-four point six two five grams pure, and ten grams at one hundred percent purity returning ten grams pure with zero impurity. The field sample_mass is a finite non-negative number for the mass of the impure sample in any consistent mass unit such as grams, milligrams, or kilograms. The field purity_percent is a finite number in the closed interval from zero through one hundred representing mass-percent purity of the target substance in that sample. Both fields may be sent as JSON numbers or as numeric strings that parse to finite values. Missing fields, non-numeric strings, NaN, Infinity, negative sample mass, and purity outside zero to one hundred fail with invalid_input and are not charged. On success the response echoes the cleaned sample_mass and purity_percent, the purity_fraction as a number between zero and one, pure_mass equal to sample mass times purity fraction, impurity_mass equal to sample mass minus pure mass, a units object documenting that pure and impurity masses share the sample mass unit, and the method and formula strings for audit trails. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where pure-mass-from-purity calculators show up in real work
Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.
Integration use cases
Bulk assay sheet conversion
Script rows of sample mass and purity percent into pure and impurity masses, catching out-of-range purities with invalid_input instead of silent clamps.
Technical questions
How is pure mass calculated from percent purity?
m_pure = m_sample × (purity_percent / 100). The purity fraction is purity_percent divided by 100; multiply that fraction by the impure sample mass.
What units does the calculator use?
Any consistent mass unit. Pure mass and impurity mass are returned in the same unit as sample_mass (grams, milligrams, kilograms, and so on).
Does 100% purity return the full sample mass?
Yes. At purity_percent = 100, pure_mass equals sample_mass and impurity_mass is zero. At 0%, pure_mass is zero.