A kilowatt (kW) measures the rate of power draw at any given moment. A kilowatt-hour (kWh) measures total energy consumed over time. Commercial bills use both — and once you can read each unit, every line on your bill makes sense.
The confusion is understandable: the names look almost identical, but they answer different questions. kW asks how hard right now? kWh asks how much in total? This guide walks through the difference, the math, and why it matters when you’re comparing electricity quotes.
Electricity uses a decimal unit system with the watt (W) at the base. Every 1,000 watts equals one kilowatt (kW). Every 1,000 kilowatts equals one megawatt (MW). Converting is straightforward:
All three — watts, kilowatts, megawatts — measure the same thing: the rate of power draw at a single point in time. None of them measure how long that draw lasts. That is what the “-hour” suffix adds.
A kilowatt-hour combines rate and time: run a 1 kW load for exactly one hour and the result is 1 kWh of energy used. Change either variable and the kWh changes:
Arithmetic examples
The pattern: kW × hours = kWh. Rearrange it to find any piece you’re missing — kWh ÷ hours gives the kW draw; kWh ÷ kW gives the run time.
Water plumbing makes the distinction concrete. Kilowatts work like the flow rate at the faucet — gallons per minute, right now. Kilowatt-hours work like the total gallons used since you opened the tap.
A wide-open faucet (high kW) fills a tank fast. A trickle (low kW) takes longer but could still fill the same tank if left running long enough (same kWh, different rate and time). Your water bill charges for total gallons — your electric bill charges for total kWh. But a commercial electric bill also charges for how wide you opened the faucet at its widest point that month. That second charge is the demand charge.
Understanding the split between kWh (total consumption) and kW (peak rate) is the foundation for reading the demand charge section of your bill .
| Unit | Measures | Where it appears on your bill |
|---|---|---|
| Watt (W) | Rate of power — the base unit | Equipment nameplates; not on bills directly |
| Kilowatt (kW) | Rate of power — 1,000 W | Demand charge line ($ per kW of peak draw) |
| Kilowatt-hour (kWh) | Energy consumed over time (kW × hours) | Energy charge line (¢ per kWh of consumption) |
| Megawatt (MW) | Rate of power — 1,000 kW | Large industrial tariffs; wholesale pricing |
| Megawatt-hour (MWh) | Energy consumed — 1,000 kWh | Wholesale market quotes; some supplier contracts |
Commercial interval meters record power draw in 15-minute intervals throughout the day. Each reading is an average kW for that window. The meter accumulates these readings and converts them to kWh totals for the billing period. Two values flow from the meter to the bill:
The sum of all 15-minute interval readings converted to kilowatt-hours. Suppliers quote a rate in cents per kWh for this portion. Delivery rates from your utility also apply per kWh. This is the part you lower by reducing overall consumption or by finding a cheaper supply rate.
The single highest 15-minute average from the entire billing month. Utilities multiply that kW number by a fixed demand rate (in dollars per kW) to produce the demand charge. This is the part you lower by flattening your peak — not by using less electricity overall, but by spreading load so no single interval spikes far above the rest.
Competitive electricity suppliers quote their supply rates in cents per kWh. That rate competes with the utility’s default supply rate — also in cents per kWh. Both apply only to the energy (kWh) portion of your bill.
The demand charge sits on the delivery side of the bill and stays fixed regardless of which supplier you choose. Switching suppliers does not reduce the demand charge. If demand charges are a large share of your bill, the most effective lever is operational — reducing your peak kW draw — not a supplier switch.
Some supplier contracts pass through capacity costs that are also tied to peak demand. When comparing quotes, confirm whether the rate is energy-only or all-in, and whether any capacity or ancillary charges are fixed or variable.
A kilowatt (kW) measures the rate of power draw at a single moment — how hard a piece of equipment is pulling electricity right now. A kilowatt-hour (kWh) measures total energy consumed over time. Run a 1 kW load for one hour and you use 1 kWh. The distinction matters on commercial bills because utilities charge for both: an energy charge in kWh for consumption and a demand charge in kW for your peak draw during the month.
Divide by 1,000. One kilowatt equals 1,000 watts. A 500-watt piece of equipment draws 0.5 kW. A 2,000-watt appliance draws 2 kW. To find kilowatt-hours, multiply the kilowatt rating by the number of hours it runs. Example: a 2 kW device running for 5 hours uses 10 kWh.
A kilowatt-hour (kWh) is the standard unit for the energy charge on a commercial bill — the line that reflects total consumption. Suppliers quote their rates in cents per kWh, and your utility's tariff applies a delivery rate in cents per kWh on top of that. Multiply the total cents-per-kWh rate by the kWh shown on your bill to get your energy cost for the month. The demand charge, billed separately in dollars per kW, covers your peak power draw.
Commercial meters record two different things. The kWh total tells the utility how much electricity flowed to your building over the month — that drives the energy charge. The kW reading captures your peak 15-minute demand — that drives the demand charge, which recovers the cost of the wires, transformers, and substation capacity sized to meet your worst-case draw. A business that runs machinery all night uses a lot of kWh; one that starts every piece of equipment at once at 7 AM creates a high kW peak. Both show up as separate line items.
A megawatt (MW) is 1,000 kilowatts. A megawatt-hour (MWh) is 1,000 kilowatt-hours. Megawatts and megawatt-hours appear in wholesale energy markets, grid capacity reports, and large industrial contracts, but most small and mid-size commercial bills still use kW and kWh. If a supplier quotes you in MWh, multiply by 10 to convert to cents per kWh (since 1 MWh = 1,000 kWh, a $10/MWh price equals 1 cent/kWh).
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