API · /molarmass-api

Molar Mass API

healthy 4,161 Subscribers

Molar-mass and stoichiometry maths as an API, computed locally and deterministically. The molarmass endpoint parses any chemical formula — with parentheses, square brackets and hydrate dots, such as Ca(OH)2, [Fe(CN)6]3 or CuSO4·5H2O — against the IUPAC conventional atomic weights and returns the molar mass in grams per mole, the total atom count and the per-element breakdown with each element's mass contribution and mass percent. The convert endpoint moves between moles, mass in grams and number of molecules for a formula, using n = mass ÷ M = molecules ÷ Nₐ with Avogadro's number. The percent endpoint gives the percent composition by mass and, for a given sample mass, the mass of each element it contains. The formula is parsed locally, so it works for any valid formula, not just compounds in a database, and is instant and private. Ideal for chemistry-education, laboratory, pharmaceutical and science app developers, stoichiometry and lab-prep tools, and STEM teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This computes molar mass from a formula; for compound database lookup use a chemistry API and for element properties an elements API.

#molar-mass #chemistry #stoichiometry #molecular-weight #moles #developer-tools

api.oanor.com/molarmass-api

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Machine-readable spec so AI agents can integrate this API.

/api/molarmass-api/openapi.json

/api/molarmass-api/llms.txt

Discovery: GET /api/index.json lists every API.

Molar Mass API — live data on the oanor API marketplace

API health

healthy

Uptime: 100.00%; Server probes · 24h
Avg latency: 75 ms; Server probes · 24h
Subscribers: 4,161; active
Total calls: 80; last 7 days

Full status page → · 16 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

3,000 calls / month
2 requests / second
Hard cap (429 above quota, no overage)
Molar mass for any formula with parentheses & hydrates
Element composition breakdown
Community support

Starter

€5.00 /month

40,000 calls / month
5 requests / second
Hard cap (429 above quota, no overage)
Everything in Free
Stoichiometry & mole conversions
Percent-composition by element
Email support

Pro

€15.00 /month

250,000 calls / month
15 requests / second
Hard cap (429 above quota, no overage)
Everything in Starter
Batch formula parsing
Isotope-aware exact mass
Priority support

Mega

€45.00 /month

1,500,000 calls / month
40 requests / second
Hard cap (429 above quota, no overage)
Everything in Pro
High-volume classroom & LMS throughput
Full stoichiometry equation balancing
99.9% uptime SLA

Built by

PremiumApi

Related APIs

Other APIs with overlapping tags.

Isotopes API

Atomic isotope reference data as an API, built on the NIST Atomic Weights and Isotopic Compositions. For every known nuclide: its element (atomic number Z and symbol), mass number, relative atomic mass, natural isotopic composition (abundance) and the element's standard atomic weight. Look an isotope up by label (C-12, U-238) or by symbol + mass, list every isotope of an element, rank isotopes by mass or natural abundance, or search. A precise physics and chemistry reference for science, education, lab and engineering apps. Distinct from element-level data.

api.oanor.com/isotopes-api

Electrolysis API

Faraday-law electrolysis maths as an API, computed locally and deterministically. The mass endpoint applies Faraday's first law of electrolysis, m = (Q·M)/(n·F) = (I·t·M)/(n·F), to give the mass of a substance deposited at a cathode or dissolved at an anode from the charge passed — or the current and time — the molar mass and the valence (electrons transferred per ion), with the Faraday constant 96485 C/mol. The charge endpoint inverts it to give the charge Q = (m·n·F)/M and, with a current, the plating time needed to deposit a target mass — the core sizing calculation for electroplating and anodising. The gas-volume endpoint computes the volume of gas evolved during electrolysis, moles = Q/(n·F) and volume = moles × 22.414 L/mol at STP, using the electrons per gas molecule (two for hydrogen, four for oxygen in water electrolysis). Molar mass is in g/mol, current in amperes, time in seconds, charge in coulombs and mass in grams. Everything is computed locally and deterministically, so it is instant and private. Ideal for electroplating, anodising, battery, hydrogen-production and chemistry-education app developers, plating-time and gas-yield tools, and electrochemistry teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is electrolysis (Faraday's laws); for cell potential and the Nernst equation use an electrochemistry Nernst API.

api.oanor.com/electrolysis-api

Colligative Properties API

Colligative-properties chemistry maths as an API, computed locally and deterministically. The freezing-point endpoint computes the freezing-point depression ΔTf = i·Kf·m and the resulting lowered freezing point of a solution, from the molality, the cryoscopic constant (1.86 °C·kg/mol for water) and the van 't Hoff factor i — which is 1 for a non-electrolyte like sugar, about 2 for sodium chloride and about 3 for calcium chloride. The boiling-point endpoint computes the boiling-point elevation ΔTb = i·Kb·m and the raised boiling point, with the ebullioscopic constant (0.512 °C·kg/mol for water). The osmotic-pressure endpoint computes the van 't Hoff osmotic pressure Π = i·M·R·T from the molarity, the temperature and the van 't Hoff factor, the pressure that drives osmosis across a semipermeable membrane, returned in atmospheres, kilopascals and bar. Molality is in mol per kg of solvent, molarity in mol per litre of solution and temperature in kelvin. Everything is computed locally and deterministically, so it is instant and private. Ideal for chemistry-education, food-science, antifreeze, desalination and biology app developers, solution and de-icing tools, and STEM teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is colligative properties of solutions; for a compound's molar mass use a molar-mass API and for dilution concentrations a dilution API.

api.oanor.com/colligative-api

Reaction Stoichiometry API

Chemical reaction-stoichiometry maths as an API, computed locally and deterministically. The limiting-reagent endpoint takes two reactants with their amounts in moles and their balanced-equation coefficients and finds which one runs out first — the limiting reagent — by comparing the moles/coefficient ratio (the reaction extent), and returns how much of the excess reagent is left over. The yield endpoint computes the theoretical yield of a product, in moles and grams, from the limiting reagent and the product's stoichiometric coefficient and molar mass, n_product = n_limiting·(coeff_product/coeff_limiting), and — given the actual yield — the percent yield. The mole-mass endpoint converts between moles, mass and the number of particles for a given molar mass, using moles = mass / molar_mass and N = moles · Avogadro's number (6.02214076e23). Amounts are in moles, masses in grams and molar masses in g/mol. Everything is computed locally and deterministically, so it is instant and private. Ideal for chemistry-education, lab, pharmaceutical and chemical-engineering app developers, reaction-planning and yield tools, and STEM teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is reaction stoichiometry; for a compound's molar mass from its formula use a molar-mass API and for solution concentrations a dilution API.

api.oanor.com/stoichiometry-api

Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for Molar Mass API?

Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Molar Mass API with the x-oanor-key header. No credit card needed for the free tier.

What's the rate limit for Molar Mass API?

Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.

How much does Molar Mass API cost?

Molar Mass API has a free tier with 100 calls / month. Paid plans start at €5.00 / month with higher quotas and faster rate limits.

Can I cancel my subscription anytime?

Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.

Is Molar Mass API GDPR-compliant?

All requests to Molar Mass API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.

Molar Mass 3

Meta 1

Pick an endpoint from the list on the left to see its details and try it.

GET /v1/convert

Mole / mass / molecules

Playground

Parameters

Custom headers

Language: Client:

GET /v1/molarmass

Molar mass of a formula

Playground

Parameters

Custom headers

Language: Client:

GET /v1/percent

Percent composition

Playground

Parameters

Custom headers

Language: Client:

GET /v1/meta

Spec

Playground

Custom headers

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Code snippets

curl https://api.oanor.com/molarmass-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."

const res = await fetch("https://api.oanor.com/molarmass-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();

$ch = curl_init("https://api.oanor.com/molarmass-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);

import requests
r = requests.get(
    "https://api.oanor.com/molarmass-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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Molar Mass API

API health

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Related APIs

Isotopes API

Electrolysis API

Colligative Properties API

Reaction Stoichiometry API

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