Percent yield calculator
Weighing 8.5 g of dried product against a theoretical 10 g gives an 85 % yield: enter both masses and get the yield, the yield fraction and the substitution written out step by step, ready for your lab report. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Actual
- 8.5
- Theoretical
- 10
- Percent yield
- 85 %
- Yield fraction
- 0.85
A percent yield calculator turns two product masses from a chemical reaction into the single efficiency figure every lab report needs. Enter the actual mass of product you isolated and the theoretical maximum mass predicted by stoichiometry; the tool returns percent yield equals actual mass divided by theoretical mass times one hundred, plus the unitless yield fraction, a readable formula string, and step-by-step substitution so you can check the arithmetic by hand.
What percent yield means for a chemical reaction
Percent yield measures how much of the stoichiometric maximum product you actually recovered after a reaction, work-up, and isolation. The defining formula is percent yield equals mass of actual product divided by mass of theoretical product times one hundred. The theoretical mass is the amount of product you would obtain if every mole of limiting reactant converted completely according to the balanced equation and nothing was lost to side reactions or transfers; the actual mass is what you weighed on the balance after purification.
Because both numerator and denominator use the same mass unit, grams cancel with grams and kilograms cancel with kilograms—you must not mix milligrams of product with grams of theoretical yield without converting first. A yield of eighty-five percent therefore means you recovered eighty-five grams for every one hundred grams that stoichiometry predicted. Yield fraction is the same ratio without the factor of one hundred, so a percent yield of eighty-five corresponds to a yield fraction of zero point eight five.
Classroom lab reports, process chemistry tickets, and green-chemistry metrics all rely on this closed definition. This calculator implements that formula only: it does not balance equations, compute theoretical mass from moles and molar mass, or look up densities. When theoretical mass is zero or non-positive the ratio is undefined, so the tool rejects the input rather than inventing an efficiency for an impossible maximum.
Practical tips, limits, and related searches
Keep both masses in the same unit before you call the tool; converting kilograms of theoretical product and grams of isolated solid yourself is outside the scope of this calculator and will produce a wrong yield if left inconsistent. Prefer sending numbers rather than pre-formatted strings when you control the client; string numbers are accepted only when they match a strict finite numeric pattern.
When actual exceeds theoretical—for instance product still wet with solvent or a transcription error that swapped fields—the tool still returns a percentage above one hundred with an explicit note instead of clamping, so automated tests can catch data-entry bugs. This landing targets people searching for a percent yield calculator, actual versus theoretical mass, or reaction yield from product masses online; it is not a limiting-reactant solver, not a moles-from-mass converter, and not a multi-step synthesis planner.
Prefer this capability when you already have both masses and only need the percent-yield figure; if your source is a word problem with reactant moles, compute theoretical mass first.
What you can do with it
Homework checks for lab percent yield
Students enter isolated product mass and stoichiometric theoretical mass from a synthesis lab and compare hand-written percent yield and yield fraction against a deterministic result before submitting the report.
FAQ
What is percent yield in chemistry?
Percent yield is (actual product mass / theoretical product mass) × 100. It reports how much of the stoichiometric maximum you recovered after the reaction and isolation.
Can percent yield be over 100%?
Yes. If actual mass exceeds theoretical mass (wet product, weighing error, or bookkeeping mistake), the result can exceed 100% and the message notes that explicitly.
Does this compute theoretical mass from moles?
Use a moles-from-mass or stoichiometry tool first if you only have reactant amounts.
Is the percent yield calculator free?
The browser tool is free and runs locally.
Can I enter milligrams for one mass and grams for the other?
No. Both masses must use the same unit, grams with grams or kilograms with kilograms. The calculator does not convert, so convert one of them first or the yield will be off by a factor of a thousand.
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/percent-yield-from-masses \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"actual_mass":8.5,"theoretical_mass":10}'const res = await fetch("https://api.kit.forhosting.com/chem/percent-yield-from-masses", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"actual_mass": 8.5,
"theoretical_mass": 10
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/percent-yield-from-masses",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"actual_mass": 8.5,
"theoretical_mass": 10
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/percent-yield-from-masses", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"actual_mass":8.5,"theoretical_mass":10}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"actual_mass":8.5,"theoretical_mass":10}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/percent-yield-from-masses", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"actual_mass": 8.5,
"theoretical_mass": 10
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.percent_yield_from_masses",
"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 | 1000000000000 |
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
When theoretical mass is zero or negative the ratio is undefined, so the API returns a clear invalid_input error instead of Infinity or a silent NaN.
How to call the API and what comes back
Actual mass must be non-negative; theoretical mass must be strictly positive—values at or below one times ten to the minus fifteen, or any non-positive theoretical mass, are treated as zero or negative and rejected. If actual mass exceeds theoretical mass the percentage can exceed one hundred and the message notes that explicitly so wet product, incomplete drying, or bookkeeping errors stay visible. Send a JSON body with two required finite numbers: actual_mass (aliases mass_actual, m_actual, experimental_mass, yield_mass, obtained_mass) and theoretical_mass (aliases mass_theoretical, m_theoretical, expected_mass, max_mass, stoichiometric_mass). Absolute values must stay within the published limit of one trillion so intermediate ratios remain finite in IEEE double precision on the Worker and in the browser. On success the response echoes rounded actual_mass and theoretical_mass, sets percent_yield to the rounded percentage, yield_fraction to the unitless ratio actual over theoretical, unit to the string percent, formula to percent yield equals m_actual over m_theoretical times one hundred, message to a short English summary, and steps to an ordered array of substitution lines. Failed validation—missing fields, non-finite numbers, values outside absolute limits, negative actual mass, or zero or negative theoretical mass—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and related searches
For teaching, pair examples: eight point five grams actual against ten grams theoretical yields eighty-five percent; four point two grams against five grams yields eighty-four percent; and theoretical mass zero demonstrates the hard invalid_input path that protects division by zero. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately set theoretical mass to zero. Round-trip checks are easy: recompute actual divided by theoretical times one hundred by hand and confirm it equals the published percent_yield within the same twelve-decimal rounding, and confirm that yield_fraction times one hundred reproduces percent_yield.
Integration use cases
Unit tests for stoichiometry software
Generate known-good sub-100%, exactly-100%, and above-100% cases plus deliberate zero-theoretical rejections for coding kata and pipeline expected values.
Batch recovery logging in process chemistry
Technicians post actual and theoretical product masses from a batch ticket and store the returned percent_yield in quality records without opening a spreadsheet.
Technical questions
What happens when theoretical mass is zero or negative?
Percent yield is undefined. This tool returns invalid_input instead of Infinity or a negative efficiency figure.