This is an open-access UK office carbon calculator.

This calculator, developed by the Clean Earth Collective, uses the latest UK Government (DESNZ/DEFRA) greenhouse gas conversion factors to estimate core operational emissions from office energy, water, waste, and digital services.
No account is required, and all assumptions are deliberately transparent and precautionary.                                                                                             

• Electricity (kWh):
  You can find this on your energy bill. A typical small office might use around 2,000–4,000 kWh per year.                                                                                                                                                                                                                                             

• Certified Green Tariff:
  If your supplier provides proof (e.g. REGO certificate), you can enter 0.
  (Note: The actual electricity still comes from the grid, so proof is essential.)

• Onsite Renewables (e.g. Solar Panels):                                                              Only enter the grid electricity you actually use. If your building is energy neutral or exports more than it uses, enter 0 rather than a negative value.(Exported energy doesn’t count as a carbon saving because it’s already part of the grid mix.)

• Heating (kWh):
  If your heating is electric, it’s usually included in your electricity bill. For gas or oil, check your fuel usage or estimate based on the building size. A small office might use around 5,000–10,000 kWh/year.

• Waste (kg):
  A full black bin bag of general waste weighs roughly 7–10 kg. If your office fills 2 bags per week, that’s about 1,000 kg/year.

• Office equipment / furniture and electronics (£):                                             These sections use industry-standard spend-based emission  factors,  so just type in your annual spend (£) on office equipment /   furniture and electronics.                                                    
•  Paper (Kg)                                                                                                       A standard ream of A4 office paper contains 500 sheets and weighs approximately 2.5kg                                                                                                                           
• Web server  (£)                                                                                                 Many web service providers have gained carbon neutral status. Enter zero if your company uses such a provider, or contact your provider to find out exact emissions. Otherwise use the UK GOV spend based factor for communications to gain a realistic estimate by entering annual cost.