How to Calculate Electricity Usage from a Submeter Fairly

The short answer

A submeter can measure a tenant, floor, machine or department's electricity use, but it does not automatically determine a fair payable bill. First calculate measured units from two dated readings. Then apply only the allocation and tariff rules that the parties and local law actually allow.

Submeter usage = closing cumulative reading − opening cumulative reading

A worked example

• Opening reading on September 1: 7,850 kWh
• Closing reading on October 1: 8,173 kWh
• Measured submeter usage: 323 kWh

The 323 kWh is evidence about energy measured by that register. It does not by itself answer:

• Which provider slab or time-of-use rate applies.
• How fixed charges, taxes or adjustments are shared.
• Whether common-area loads belong to the tenant.
• Whether resale or markup is permitted.
• Whether the submeter has a multiplier.

Those are policy, contract and legal questions—not meter arithmetic.

Separate four layers

Keeping these layers separate makes a disagreement diagnosable. If the units match but the amount does not, the issue is allocation or pricing rather than the physical reading.

Boundaries matter more than monthly labels

Take opening and closing readings at the actual handover or agreed cutoff. A September rent period and a provider bill dated August 18–September 17 do not align automatically. Prorating requires an explicit method and should be labelled as an estimate unless exact boundary readings exist.

Shared meters and common areas

If one main meter covers several units, individual submeters may not sum exactly to the main meter because of common loads, different boundaries, meter accuracy, losses or omitted circuits. Do not quietly assign the residual to one occupant.

Document:

1. Which circuits each submeter covers.
2. The reading schedule and precision.
3. Who can verify the readings.
4. How common usage and fixed charges are handled.
5. What happens after replacement or access failure.

Privacy and evidence

Share only the relevant property, meter, dates, cumulative values and calculation. Provider customer identifiers and other tenants' usage may not belong in a shared spreadsheet or message.

A clean MeterPilot setup

Create the property first, then name each submeter by the space or equipment it actually measures. Preserve opening observations and use the same cutoff schedule. MeterPilot can keep the measured histories distinct; it should not invent a tariff, legal entitlement or shared-cost rule.