How to calculate a dorm or rental electricity bill 2026 — step by step, with a worked example
A landlord's bill is not calculated the way a utility bill is. It is far simpler — which is exactly why it is easy to check. This page walks from reading the meter to a difference figure you can actually put to the landlord.
Calculating a dorm bill takes two lines: (this month's meter reading − last month's) = units used, then multiply by the per-unit rate in your lease. There are no tiers, no separate Ft line and no monthly service charge — because it is not a utility bill, it is a resale by the landlord. The line people forget is the third one: what did it actually cost? A room using 190 units in the month costs the utility about 761 THB in total (4.01 THB/unit, with the progressive energy charge, Ft of 0.1623, the 24.62 THB service charge and VAT all included). At a landlord rate of 8 THB/unit the same month is 1520 THB — a gap of 759 THB a month, roughly 9103 THB a year — and at the 4.88 THB/unit ceiling in the 2025 OCPB notification it would be 927 THB. The full utility-side formula is at how to calculate an electricity bill 2026; the rate you should be paying in a rental is at rental electricity per unit.
Three steps to do it yourself
Steps one and two are what the landlord does. Step three is the one they do not show you, and the only one that tells you whether the price you pay is reasonable.
Step 1 — find the units actually used
Take this month's meter reading and subtract last month's. The example used throughout this page: 7,850 − 7,660 = 190 units. On a mechanical meter read only the black digits; the red decimal window is not counted. How to read each meter type: reading an electricity meter.
Step 2 — multiply by the rate in the lease
190 units × 8 THB = 1520 THB. That is the whole calculation — no Ft to add, no service charge, no separate VAT on top. If your bill carries those lines on top of an already-flat rate, ask what they are based on, because that is double counting.
Step 3 — compare against the real cost
The same units on a utility bill come to 761 THB, or 4.01 THB/unit when divided back. The difference is 759 THB in a single month, and it is still above the 4.88 THB/unit ceiling (= 927 THB). That difference is the figure you can put to the landlord, or attach to a complaint, straight away.
The comparison by monthly consumption
The real-cost column is computed from the full residential tariff (tiers + Ft 0.1623 + service charge + VAT), so it moves with consumption, while a landlord's flat rate does not. That is why the gap looks harshest in percentage terms for the lightest users.
| Monthly use | Real total bill (THB/unit) | At the 4.88 THB ceiling | At 8 THB/unit |
|---|---|---|---|
| 90 units | 342 THB (3.80) | 439 THB | 720 THB |
| 120 units | 466 THB (3.88) | 586 THB | 960 THB |
| 190 units (this page's example) | 761 THB (4.01) | 927 THB | 1520 THB |
| 200 units | 808 THB (4.04) | 976 THB | 1600 THB |
How to read it: the bracketed figure is baht per unit obtained by dividing the whole bill, not the price of any single tier. The 3.95 THB/unit system-wide average often quoted in the news means something else again and cannot be compared directly against one room's bill. For your own number, enter your units in the electricity bill calculator, or let the rental electricity checker compute the gap for you.
Five places the number usually goes wrong
Before concluding you are over-charged, check these five, because some discrepancies are technical rather than deliberate — and knowing which is which ends the conversation faster.
Meter rollover. A five-digit meter that fills up restarts from zero, so this month's figure can be lower than last month's. The fix is to add 100,000 (or whatever the digit count implies) before subtracting — not to conclude the meter is broken.
Readings taken on different days. If the landlord reads on the 25th and you read on the 1st, the unit counts will naturally disagree. Ask which day the reading cycle falls on, then read on that same day two months running so the comparison is like for like.
A minimum-units clause. Some leases require a minimum — say 50 units — even when actual use is lower, which pushes the effective baht per unit far above the written rate. Always compute from the amount actually paid divided by the units actually used.
One meter shared across rooms. If your room shares a meter with common space or a water pump, the units recorded are not yours alone. Ask for the split method in writing, otherwise the figure is unverifiable from the outset.
Water or common-area charges folded into one total. If the bill is not itemised, do not divide the total by electricity units — the resulting baht-per-unit is inflated. Ask for separate lines first, then compute. A landlord who refuses to itemise creates a transparency issue that is itself complainable: see how to report over-charged rental electricity.
If the gap survives all five checks, the number is solid enough to raise. Keep the two months of meter photos and the bills as evidence, then see where your rate sits against the 4.88 THB/unit ceiling at rental and dorm electricity. If you are in a condo and still unsure who issues your bill, start at condo electricity cost per unit.
Who wrote this
Frank Lee, Founder of CapSolar — a commercial solar design-and-build company in Thailand with 80+ MWp installed across 150+ projects, 100+ clients served and 85K+ tons of CO₂ avoided. Reading meters and unpicking building bill structures is weekly work here. Every figure on this page is computed from the same official rate set that drives the site's electricity bill calculator, not typed in by hand.
FAQ
Read next
How to read an electricity meter
Dial and digital meters — which digits to read
Rental electricity per unit 2026
What you should pay, and the 4.88 THB/unit ceiling
Where to report over-charging
Evidence, channels and the filing steps
How to calculate an electricity bill 2026 (utility side)
Tiers, Ft, service charge and VAT — the full formula
Own a rental building? Cutting the real power cost beats marking up tenants
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