Carbon Emissions API: Calculate CO2e in Code, Free

Most emissions APIs ask you to sign up before you can see a single number. The ZeroCarbon emissions API does not: its calculation endpoints answer anonymous requests, rate-limited, so you can test the numbers before you build on them. This guide shows the four calculators with real requests and responses.

Your first request: grid electricity

Send the kWh and the country. Scope 2 is calculated with that country's published grid factor for the current edition.

curl -X POST https://zerocarbon.org.in/api/v1/calculate/electricity \
  -H "Content-Type: application/json" \
  -d '{"kwh": 145000, "country_code": "IN"}'

{
  "success": true,
  "data": {
    "emissions_kg_co2e": 97875,
    "emission_factor": 0.675,
    "emission_factor_label": "0.675 kgCO2e/kWh (CEA_CO2_Baseline_v22_FY2025-26 (weighted_average, AR5))",
    "emission_factor_source": "CEA_CO2_Baseline_v22_FY2025-26",
    "scope": "scope_2",
    "activity": { "value": 145000, "unit": "kWh" },
    "formula": "145000 kWh × 0.675 kgCO2e/kWh = 97875.0000 kgCO2e"
  }
}

The factor label names the publisher and edition: here the Central Electricity Authority's CO2 Baseline Database, version 22, for FY 2025-26. Send GB instead and you get the UK DESNZ factor; the UK factor guide explains the 2026 change.

The four calculators

Fuel, in Python

import requests

r = requests.post(
    "https://zerocarbon.org.in/api/v1/calculate/fuel",
    json={"fuel_type": "diesel", "amount": 1000, "unit": "L", "country": "IN"},
)
print(r.json()["data"]["emissions_kg_co2e"])   # 2687.954

1,000 litres of diesel is 2,687.954 kg CO2e at India's factor of 2.687954 kg per litre: 2.68 kg CO2 plus methane and nitrous oxide at AR5 warming potentials. The DG set guide shows how to get the litres right.

Flights and freight, in JavaScript

const post = (path, body) =>
  fetch("https://zerocarbon.org.in" + path, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(body),
  }).then((r) => r.json());

// One traveller, 1,150 km one way: medium haul, 148.35 kg CO2e
await post("/api/v1/calculate/flight", { distance_km: 1150, passengers: 1, country: "IN" });

// 10 tonnes by road over 500 km: 5,000 t-km, 445 kg CO2e
await post("/api/v1/mcp/tools/calculate_freight_emissions",
  { mode: "road", weight_tonnes: 10, distance_km: 500, country: "IN" });

When the API says no

An emissions figure with the wrong factor is worse than none, so the API refuses inputs it cannot price and says what to send instead.

{
  "success": false,
  "error": "There is no published factor for \"kerosene\" in the library yet.",
  "code": "unsupported_input",
  "guidance": "Supported fuel_type values: petrol, diesel, natural_gas, lpg, coal, cng, furnace_oil."
}

• No country: HTTP 400. Factors are national and no default is assumed.
• An unknown fuel or mode: HTTP 422 with the accepted values.
• A flight with no distance: refused. Route distances are not estimated, so send the great-circle distance in km.

With an API key

A key from your ZeroCarbon workspace raises the limits, falls back to your company's country when a request omits it, and unlocks the ledger endpoints: records, drafts, documents and suppliers. Send it in the Authorization header as a Bearer token. The full reference is in the developer docs.

For AI agents

The same calculators, plus EU CBAM default values and BRSR Core GHG indicators, are exposed as an MCP server at https://zerocarbon.org.in/api/v1/mcp (Streamable HTTP). Add it as a custom connector in Claude or ChatGPT, or in Cursor's MCP settings, with no key. Each tool returns structured results with its output schema.