There is no single price for factory electricity. The price per unit depends on which customer category the factory is in (measured by maximum power demand, not by type of business), which voltage level it takes supply at, and whether it is billed at one price all day under the normal rate or at two prices by time of day under TOU. The amount actually paid also includes the monthly service charge, the Ft charge (the part of the bill adjusted by an automatic formula and added every month) and value added tax, and for categories 3–4 there is also a demand charge that does not depend on the number of units. Two factories can therefore pay different amounts per unit without the utility having made any mistake.
The rate figures in this article come from the business tariff announcement of PEA (Provincial Electricity Authority) in effect from the September 2026 billing month. They show category 2 at both medium and low voltage, and categories 3–4 at low voltage only. They are rates before Ft and value added tax.
| Variable that changes the per-unit figure | How it works |
|---|---|
| Customer category | Opens a different rate table |
| Voltage level of supply | A different row in the same table |
| Rate type (normal or TOU) | A different billing structure |
| Number of units and time of use | The energy charge per unit is not a single value |
| Demand charge and monthly service charge | Amounts that do not fall with fewer units |
| Ft and value added tax | Added on top of the rate table |
Which category is your factory in, and what decides it
The customer category is measured by the maximum power demand passing through a single meter, not by the type of business or the size of the building. Two factories making the same product can therefore sit in different categories and read from different rate tables.
Before you can know the price per unit, you need to know which table you are in, because the utility does not have one price for every factory. It divides customers into categories, and each category has its own rate table. What decides the category is not what you make or how large the factory is, but the maximum power the factory draws from the line each month, which is called power demand.
In the PEA announcement, a small business is defined in these words: “as well as related premises, with a maximum 15-minute average power demand below 30 kilowatts, connected through a single meter”
In plain terms: the utility does not look at the momentary power when a machine starts up. It looks at the highest 15 minutes average power demand in the month, passing through a single meter, and compares that value with the business-size thresholds.
The thresholds have two axes: power demand, and units consumed per month. The units axis uses an average over several months, not a single month. The same thresholds apply at both PEA and MEA (Metropolitan Electricity Authority).
- Power demand
- The maximum power the factory draws from the line in a month, calculated as an average over a short interval as specified, not a momentary value. Measured in kilowatts. Used both to assign the customer category and as a billing line for medium and large businesses.
- Voltage level
- The voltage of the line the utility supplies to the factory, divided into low, medium and high. Each level is a separate row in the rate table of the same category.
| Customer category | Maximum power demand | Electricity consumption |
|---|---|---|
| Category 2 (small business) | Below 30 kW | No units threshold |
| Category 3 (medium business) | From 30 kW but below 1,000 kW | Average consumption over 3 months not exceeding 250,000 kWh/month when expressed as units per month |
| Category 4 (large business) | 1,000 kW or more | Or average consumption over 3 months exceeding 250,000 kWh/month when expressed as units per month |
Suppose two food factories make the same product. One runs its machines in groups, its maximum power demand stays below the threshold, and it is in category 2. The other switches everything on at once, reaches the threshold, and is in category 3. These two factories open different rate tables from the start. The difference in their per-unit figures begins here, not with a billing error by the utility.
Once you know the category, you need two more things before opening the table: which voltage level you take supply at, and whether you are on the normal rate or TOU. Within the same category's table, each voltage level and each rate type is a separate row with a separate price.
Category 2 (small business): how much per unit, and why it is not a single value
Category 2 at the normal rate is billed in tiers by number of units at low voltage, and at a single price for all units at medium voltage. TOU has two prices by time of day. The per-unit figure for a small business therefore changes with how many units it uses, which voltage level it takes supply at, and which rate type it is on.
Before opening the table, one thing makes life easier: the rate figures at PEA and MEA are the same. Although the same voltage level name covers a different kilovolt range at the two utilities, they serve in parallel, so the figures below apply whichever utility serves your factory (read more about the two utilities).
For category 2 at the normal rate, low voltage, the price per unit is not one value but a staircase: the first units of the month are billed at one price, the next units at a higher price, and units beyond that at a higher price again. Medium voltage is billed at one price for every unit. On TOU, there are two prices by time of day instead.
| Rate type · voltage level · unit range | Energy charge for category 2 (small business) |
|---|---|
| Normal rate · low voltage · first units up to 150 kWh/month | 3.2484 THB/kWh |
| Normal rate · low voltage · next units up to 400 kWh/month | 4.2218 THB/kWh |
| Normal rate · low voltage · units beyond that | 4.4217 THB/kWh |
| Normal rate · medium voltage · all units | 3.9086 THB/kWh |
| TOU · low voltage · On Peak | 5.7982 THB/kWh |
| TOU · low voltage · Off Peak | 2.6369 THB/kWh |
| TOU · medium voltage · On Peak | 5.1135 THB/kWh |
| TOU · medium voltage · Off Peak | 2.6037 THB/kWh |
The staircase means that two shops both in category 2 at the normal rate, both at low voltage, get a different per-unit figure when they divide their bills, simply because they use a different number of units. The shop using less has most of its units in the first tier; the shop using more has many units in the more expensive tiers. And if another shop takes supply at medium voltage, it is immediately a different row and a different price.
For category 2 customers on TOU, the price per unit depends on when the electricity is used. The same unit in the On Peak period and the Off Peak period is billed at different prices, so the average figure reflects each site's own usage mix and is not a fixed value that can be compared directly. Whether switching to TOU is worthwhile, and how to work out the break-even point, is covered in the article on whether to switch to TOU
Tiered energy charge for small business, normal rate, low voltage
Categories 3 and 4 at low voltage: why the bill divided by units is higher than the per-unit price in the table
Category 3 at the normal rate (for existing customers), low voltage, has both an energy charge per unit and a demand charge per kilowatt. TOU for categories 3 and 4 at low voltage bills energy at two prices by time of day and has a demand charge line for the On Peak period. The bill divided by units is therefore always higher than the energy charge.
Categories 3 and 4 have a line that category 2 does not: the demand charge, billed in baht per kilowatt of the maximum power the factory draws, not by number of units. The factory therefore pays two amounts: one that grows with units, and one that grows with maximum power. When the total is divided by units, the result is always higher than the energy charge per unit in the table, and factories with different maximum power draw get different per-unit figures even when they use the same number of units.
The normal rate for categories 3–4 is for existing customers. New customers entering these categories are placed on TOU (how categories 3, 4 and 5 differ).
TOU splits the price per unit by time of day, and holidays count as Off Peak (which periods are On Peak / Off Peak). For the demand charge, the normal rate uses the maximum for the whole month, while TOU uses only the maximum in the On Peak period (how it is measured and billed).
| Category and rate type · item | Price (low voltage) |
|---|---|
| Category 3 normal rate · energy charge, all units | 3.1751 THB/kWh |
| Category 3 normal rate · demand charge per kilowatt | 221.50 THB/kW |
| Category 3 TOU · energy charge, On Peak | 4.3297 THB/kWh |
| Category 3 TOU · energy charge, Off Peak | 2.6369 THB/kWh |
| Category 3 TOU · demand charge, On Peak, per kilowatt | 210.00 THB/kW |
| Category 4 TOU · energy charge, On Peak | 4.3297 THB/kWh |
| Category 4 TOU · energy charge, Off Peak | 2.6369 THB/kWh |
| Category 4 TOU · demand charge, On Peak, per kilowatt | 210.00 THB/kW |
Suppose Factory A and Factory B are both in category 3 on TOU at low voltage and use the same total units per month, but A runs heavy loads during On Peak while B moves its heavy work to Off Peak. B has more units billed at the Off Peak price and a lower maximum power demand in the On Peak period. B's bill is lower than A's even though the units are the same. This is why you cannot compare per-unit figures with another factory without knowing when they use electricity and how much maximum power they draw.
Category 4 on TOU at low voltage has the same structure as category 3 on TOU, but it is its own table. Whenever a factory moves from category 3 to 4, the whole new table must be read. This article lays the two tables side by side for comparison only and does not conclude which category is cheaper, because the actual amount depends on each factory's usage mix.
Energy charge per unit for medium business, low voltage — normal rate versus TOU
Which lines do not fall with fewer units, and why the figure in the table is not the figure you pay
The monthly service charge is a fixed amount that differs by category and voltage level. The amount actually paid is the charge at the tariff rate, plus Ft, plus value added tax, and the rates in the table do not include tax. To compare per-unit figures with another factory, you have to compare the same layer of the bill.
Every category has a monthly service charge as a fixed amount that does not depend on the number of units and differs by category and voltage level. MEA states that this charge is payable even in a month with no consumption; PEA does not state this in its tariff announcement. Category 4 also has a monthly service charge line, with the figure in the category 4 rate table.
- Monthly service charge
- A fixed amount collected every month according to category and voltage level, independent of the number of units used.
| Category and voltage level | Monthly service charge |
|---|---|
| Category 2 (small) · low voltage · normal rate and TOU | 33.29 THB/month |
| Category 2 (small) · medium voltage · normal rate and TOU | 312.24 THB/month |
| Category 3 (medium) · low voltage · normal rate and TOU | 312.24 THB/month |
Suppose a factory has a month of maintenance shutdown and uses far fewer units. The same monthly service charge is divided by fewer units, so the per-unit figure comes out higher than in a normal month, even though nothing in the rate table changed. The demand charge for categories 3–4 pushes the average up in the same way, because it does not fall with fewer units.
The next layer is what is added on top of the rate table. The PEA announcement states: “2. The electricity charge billed each month consists of the electricity charge at the above rates, the electricity charge under the automatic tariff adjustment formula (Ft)” Ft is a fixed rate per unit added to the bill every month and revised by period (what is Ft (in Thai)). On top of the whole amount, value added tax of 7% is added as another layer, because the rates in the table do not include tax.
So the per-unit figure in the rate table is the bottom layer of the bill, and the amount actually paid divided by units is the top layer. If you compare your own top layer with the table figure a colleague quotes, the numbers will not match, and nobody has made a mistake. When comparing, ask clearly whether the other party means the energy charge in the table or the amount actually paid divided by units.
Categories 3–4 also have a minimum charge, which must not be less than 70% of the maximum demand charge in the past 12 months, counting up to the current month (the mechanism is in the demand charge article). And for customers billed a demand charge, there is a power factor charge as another line that is not billed per unit.
Another reason your own per-unit figure is higher than the table, even though your category and voltage level match the factory next door, is when you own your own transformer and the meter is installed on its low-voltage side. PEA states: “Note 1. Where the meter is installed on the low-voltage side of a transformer that is the property of the customer, the kilowatts and the billable units shall be increased by 2 percent” In other words, both units and kilowatts are increased by a percentage before billing, and the bill does not say which bills have been adjusted, so this has to be confirmed with the utility. This rule is in the PEA announcement. If a month's bill rises even though the number of units is the same, the possible causes are gathered in the article on bills rising while kWh stays the same
✗ The single average electricity price per unit reported in the news is the price a factory pays per unit
✓ A factory has its own table according to category, voltage level and rate type, and the amount actually paid has Ft and value added tax added on top. A single average figure is therefore not the per-unit price of any particular factory.
One month with a high peak: how long does it change your rate table
A category 2 factory whose power demand reaches the threshold in any month is moved up to category 3, 4 or 5, and can only move back once that value stays below the threshold for the specified number of consecutive months. In the meantime it is billed at the rates of the category it was moved to.
Category 2 applies only while the small business's power demand stays below 30 kW. In any month where the month's maximum reaches this threshold, the factory is moved up to category 3, 4 or 5 as the case may be, and opens a new rate table with a demand charge line that the old table did not have. This rule applies at both PEA and MEA.
Moving back does not happen as soon as the next month's consumption drops. The factory can return to category 2 only when power demand stays below 30 kW for 12 months in a row, and throughout that period it is still billed at the rates of the category it was moved to.
For whoever manages the electricity bill, this means a single peak month does not just make that month's bill expensive; it changes the table used for billing for several months afterwards. If your factory is in category 2 and has a month where power demand comes close to the threshold, the per-unit figure that changes in later months may come from a change of table, not from a change of prices in the old table. How the categories you can be moved to bill differently is covered in the article comparing categories 3, 4 and 5