How to Calculate Dormitory Water & Electricity Bills (Meter to Invoice)
Published June 5, 2026 · 8 min read
Utilities are the fiddliest, most error-prone part of running a dorm — a wrong rate, a miscounted unit, or a forgotten arrear costs you money or breaks the law. This is a practical how-to you can actually follow: set rates once, record meters room by room, then produce the whole dorm's bills on one page — with a line-by-line worked example for a single room.
TL;DR
- Set per-unit electricity/water rates once — the system remembers them every month, no re-typing
- Water can be billed three ways: by meter / flat per room / included in rent — set it dorm-wide or per room
- Recording meters = type the current reading per room; the system pulls last month's reading and computes (current − previous) × rate automatically
- Bill the whole dorm on one page — the system bundles rent + water + electricity + other charges + carried-forward arrears
- Core formula: units used × price per unit — and by Thai CPB law, you can't charge more than the public provider's actual rate
Step 1 — set rates + pick how to bill water (once)
Before billing, store the per-unit price of electricity and water in the system, then choose how water is billed — three options:
Read a water meter like the electric one and charge by actual units used (THB/m³) — the fairest, and in line with CPB guidance.
Best for dorms with per-room water meters
A fixed water charge per room per month (e.g. ฿100), no water meter reading needed — the system adds it to each bill.
Best for dorms without per-room water meters
Water isn't billed separately — it's treated as part of the rent, and the bill shows no water line.
Best for dorms that already fold water into rent
⚠️ Under Thai CPB Notice 2018, owners may charge water/electricity only at the rate the public utility actually charges — no markup. The system warns you if a rate exceeds a rough cap (electric ~฿5/unit, water ~฿18/m³). You can also set a minimum water/electric charge if you need one.
Step 2 — record meters monthly
Once rates are set, the monthly job is just reading meters — open the meters page and do these three things:
- 1
Pick the month to record
The system lists occupied rooms grouped by building/floor, so you can walk and read in order.
- 2
Type the current reading per room
Last month's reading is pulled in automatically — you just read the dial and enter the latest number. Each room autosaves.
- 3
The system computes units + cost instantly
Units used = current − previous, multiplied by your rate. You see each room's water/electric cost right as you record — no separate calculator.
No meter swap needed — old dial meters work fine. You read the number and enter it yourself (the system doesn't guess from a photo, so the figures on the bill are accurate).
Step 3 — bill the whole dorm on one page
Once meters are in, go to the billing page — the system assembles every room's bill at once:
- 1
The system bundles everything automatically
It pulls each room's rent + the water/electric you recorded + other charges (e.g. common-area, garbage, parking) into a single total per room.
- 2
Adds carried-forward arrears + late fees (if any)
If a room owed money last month, the system rolls it into the new bill and applies your late-fee rule — no manual chasing.
- 3
Review, then issue for the whole dorm
The due date is set automatically to the day you configured (e.g. the 5th). Issue every bill in one click, then send them to tenants.
💡 Want to send bills to tenants on LINE with a pay link? See the 'Send bills via LINE' article at the bottom of this page.
Worked example — one room (meter mode)
Say a room with ฿3,000 rent, electricity at ฿5/unit, water at ฿18/m³:
Units used = current reading − last month's reading · every line rounds to whole baht (no satang), exactly like the real invoice.
Try the free utility calculator
Enter meter readings and per-unit prices, see the water/electric total instantly — no signup, no email.
Open the calculatorFAQ
Do I need to switch to digital meters first?
No. Old dial meters work fine — you just read the number and enter it. If you're weighing whether to invest in new meters, see the meter cost-comparison article at the bottom of this page.
Can I charge more for electricity than the utility charges?
No. Under CPB Notice 2018, water/electricity must be charged at the public provider's actual rate — no markup. The system warns you if a rate exceeds a rough cap. If your costs rise, the lawful route is to adjust rent instead (see the new-rent article).
Can I bill water as a flat fee without reading a meter?
Yes. Choose 'flat per room' and set a fixed monthly amount — the system adds it without any water-meter reading. Or if water is already part of the rent, choose 'included in rent' and the bill shows no water line.
Can I set a minimum water/electric charge?
Yes. If your dorm has a minimum (e.g. low usage is still billed at the minimum), set it in the system and it's applied automatically at billing time.
What if I forgot to record last month's meter?
The system uses the latest available reading as the baseline — if last month is missing, fill it in before billing so units are correct. Recording every month, consistently, is the most accurate approach.
Can I try the math before signing up?
Yes. There's a free utility calculator — enter meter readings and rates and see the total instantly, no signup (link below).
Let the software calculate utilities + bill the whole dorm
Record meters room by room, the system computes units and issues every bill, and you can send via LINE — all in one place. Free 30-day trial, no card.
Start free trialSources
Water/electricity rates follow the public authorities' published tariffs — check the latest here:
- Electricity tariff — Metropolitan Electricity Authority (MEA)
- Water tariff — Metropolitan Waterworks Authority (MWA)