Guide
A customer asked for your carbon footprint. Here's what to send.
Send a GHG Protocol-aligned carbon footprint with your Scope 1, 2 and 3 totals, the reporting period, what's included and excluded, and the emission factors you used with their sources. That list follows what the GHG Protocol Corporate Standard requires an emissions report to state, so your customer can use your numbers in their own reporting.
What to do, step by step
- Confirm what your customer asked for. Ask which scopes they need, which period it should cover (a calendar year or their fiscal year), and whether they want your whole footprint or only the share tied to what you sell them. Requests through CDP's supply chain program can cover emissions allocated to a specific customer. Then tell them what you can provide and by when.
- Gather the documents. Pull utility bills, fuel receipts, and shipping and waste invoices for the whole period. Read the usage on each one (kWh, therms, gallons), not the dollar amount. The documents guide lists each record, where the number sits and which scope it covers.
- Calculate and label every line. Multiply each quantity by a published emission factor and record the factor's source and edition. Label each line measured, calculated or estimated, as our methodology describes. List what you left out and why, and put the totals by scope, the period and the exclusions on the first page.
Why customers are asking
Your customer is counting their supply chain. Under the GHG Protocol Scope 3 Standard, a company's Scope 3 includes the upstream emissions from producing the goods and services it buys (Category 1, purchased goods and services). The emissions from making what you sell them are part of that number.
Many requests arrive through CDP. More than 200 organizations are members of CDP's supply chain program, which they use to ask chosen suppliers to disclose environmental data. Members then use those answers in their own reporting and Scope 3 accounting.
California adds a deadline for the largest companies. SB 253 applies to companies formed in the US that do business in California and have more than $1 billion in total annual revenue. CARB has set November 10, 2026 as the deadline for their first Scope 1 and 2 reports. Its July 2026 workshop slides list Scope 3 reporting from 2027, and CARB is still writing the rules for it.
The law does not reach a small business. If a customer asks you, it is because they need your numbers for their own report, not because SB 253 requires you to file one.
Worked example: one month of bills
Worked example
A small US shop's bills for one month show 3,850 kWh of electricity and 186 therms of natural gas. Purchased electricity is Scope 2. Gas burned on site is Scope 1.
| Electricity used (Scope 2) | 3,850 kWh |
|---|---|
| Electricity factor | 770.884 lb CO₂e/MWh × 0.45359237 kg/lb ÷ 1,000 kWh/MWh = 0.349667 kg CO₂e/kWh, rounded to 0.350 |
| Electricity emissions | 3,850 kWh × 0.350 kg CO₂e/kWh = 1,347.50 kg CO₂e |
| Natural gas used (Scope 1) | 186 therms |
| Gas factor | 5.31145 kg CO₂e/therm |
| Gas emissions | 186 therms × 5.31145 kg CO₂e/therm = 987.93 kg CO₂e |
| Total | 1,347.50 + 987.93 = 2,335.43 kg CO₂e, about 2.34 tonnes |
This example uses the US national average. eGRID also publishes a rate for each grid subregion, which can be higher or lower where you are, so name the factor you used.
Frequently asked questions
Do I need Scope 3?
Not always. The GHG Protocol Corporate Standard requires Scope 1 and 2 and treats Scope 3 as optional, so start with what your customer asked for. If they want Scope 3, include the categories you have documents for, such as shipping, waste and business travel, and list the ones you left out.
Does it have to be verified?
It depends on your customer, so check what they specify. The GHG Protocol Corporate Standard does not require third-party verification; it lists external assurance as optional information in an emissions report. CDP's 2025 corporate questionnaire asks for the verification status of each scope, offers an answer for emissions with no third-party verification or assurance, and describes verification as good practice. Some customers ask for verification, sometimes called assurance, by an independent firm. If yours does, ask which standard they expect before you hire anyone. A CarbonKick report is a self-reported estimate and is not third-party verified.
The request came through CDP. What do I do?
Answer it in CDP's questionnaire. A supplier responding to a customer's request can also answer supply chain questions specific to that customer, in addition to the main questionnaire. The numbers come from your footprint, so finish that first.
Does SB 253 apply to my small business?
No. SB 253 applies to companies formed in the US that do business in California and have more than $1 billion in total annual revenue. Those companies report their own emissions, with Scope 3 expected from 2027, and Scope 3 includes what they buy. That is why a covered customer may ask you for data. The request comes from your customer, not from the law.
Sources
- The Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard, revised edition, WRI and WBCSD, 2004. Chapter 9, Required information, and Optional information (external assurance).
- Corporate Value Chain (Scope 3) Accounting and Reporting Standard, WRI and WBCSD, 2011. Category 1: Purchased goods and services.
- CDP Supply Chain Membership, CDP, accessed October 30, 2026. How membership works and how suppliers respond.
- Full Corporate Questionnaire, Module 7, CDP, April 2025. Question 7.9, verification/assurance status of reported emissions.
- Corporate Disclosure of Climate Data, California Air Resources Board, accessed October 30, 2026. Who SB 253 covers, the November 10, 2026 deadline, and the rules for 2027 and later.
- SB 253 Public Workshop: California Corporate Greenhouse Gas Reporting Program, California Air Resources Board, July 2026. Slide 4: Scope 1 and 2 in 2026; Scope 1, 2 and 3 in 2027 and after.
- eGRID Summary Data, eGRID2023 revision 2, US EPA, released June 12, 2025. U.S. total output emission rate, 770.884 lb CO₂e/MWh.
- GHG Emission Factors Hub, US EPA, 2025. Table 1, Stationary Combustion, natural gas.
Get your footprint from the bills you already have
Gather what you can find. CarbonKick reads the usage on each document and returns a GHG Protocol-aligned footprint in minutes, with every line labeled measured, calculated or estimated. Send me what you have and I'll run your numbers free and walk you through them.
How CarbonKick calculates: read the methodology →
About the author: Mark Alvarado is an environmental engineer and the founder of CarbonKick. Before building it, he calculated carbon footprints by hand for consumer brands.