Electrical Abbreviations Explained
Reading a datasheet, choosing a power supply, or decoding an electricity bill requires knowing what W, kVA, PF and kWh actually mean and how they relate. This reference covers the terms you encounter most in residential and maker electrical work.
Abbreviations quick reference
| Abbreviation | Full name | Unit / Formula | Typical context |
|---|---|---|---|
| W | Watt | Power = V x A | Appliance power ratings, light bulbs, heaters |
| kW | Kilowatt | 1 kW = 1,000 W | Boiler output, EV charger speed, generator rating |
| MW | Megawatt | 1 MW = 1,000,000 W | Grid-scale power stations, large industrial loads |
| VA | Volt-ampere | Apparent power = V x A | UPS sizing, transformer ratings, generator apparent output |
| kVA | Kilovolt-ampere | 1 kVA = 1,000 VA | Generator specs, distribution transformer ratings |
| PF | Power factor | PF = W / VA (range 0 to 1) | Efficiency of AC loads; motors and switching PSUs often 0.6-0.9 |
| Wh | Watt-hour | Energy = W x hours | Small battery capacity, portable power stations |
| kWh | Kilowatt-hour | 1 kWh = 1,000 Wh | Electricity billing unit, EV battery capacity (e.g. 60 kWh pack) |
| Ah | Ampere-hour | Capacity = A x hours | Car batteries, lead-acid, lithium cell specs |
| mAh | Milliampere-hour | 1 Ah = 1,000 mAh | Phone batteries, AA cell ratings, USB power banks |
| AC | Alternating current | Current reverses direction at the supply frequency | Mains power (230 V / 50 Hz in Europe, 120 V / 60 Hz in North America) |
| DC | Direct current | Current flows in one direction only | Batteries, USB, solar panels, 12 V vehicle wiring |
| V | Volt | Electrical potential difference | Mains voltage, battery voltage, signal levels |
| A | Ampere (amp) | Rate of charge flow | Fuse ratings, charger output, motor current draw |
| mA | Milliampere | 1 A = 1,000 mA | LED current (typically 20 mA), sensor supply, logic signals |
| Ohm (O) | Ohm | Resistance = V / A | Resistor values, cable resistance, heating element specs |
| AWG | American Wire Gauge | Standardised wire diameter scale (lower = thicker) | North American wiring; common in maker/electronics datasheets worldwide |
| RMS | Root mean square | Effective AC value = peak / sqrt(2) for a sine wave | Multimeter AC readings, mains voltage spec (230 V RMS in Europe) |
| Hz | Hertz | Cycles per second | Mains frequency (50 Hz EU / 60 Hz US), motor speed, PWM frequency |
| kHz | Kilohertz | 1 kHz = 1,000 Hz | Switching PSU frequency, audio range, PWM in motor controllers |
Formulas you will actually use
P = V x I: Watts from volts and amps
Real power in watts equals voltage multiplied by current. A 230 V appliance drawing 8 A consumes 1,840 W (1.84 kW). This formula applies directly to DC circuits and to resistive AC loads like heaters and incandescent bulbs. For AC loads with motors or switching supplies, multiply the result by the power factor to get true watts.
kWh = kW x hours: Energy for cost calculation
Multiply the power in kilowatts by the number of hours the device runs. A 2 kW kettle used for 30 minutes (0.5 h) uses 1 kWh. At 0.30 EUR/kWh that costs 0.30 EUR. This is the unit on your electricity bill, so this formula connects appliance wattage directly to what you pay.
VA = V x A: Apparent power for generators and UPS
Apparent power in volt-amperes is voltage multiplied by current without accounting for phase difference. Generators and UPS units are rated in VA or kVA because they must supply the full current the load draws, regardless of the power factor. A UPS rated at 1,000 VA does not necessarily deliver 1,000 W to the load.
kW = VA x PF: Real power from apparent power and power factor
To convert a VA or kVA rating to real watts, multiply by the power factor. A 5 kVA generator powering loads with PF 0.8 delivers 4 kW of usable power. Motor loads and switch-mode power supplies typically have PF between 0.6 and 0.95; pure resistive loads have PF 1.0.
Voltage drop: Vdrop = I x Rcable
Voltage drop equals load current multiplied by the cable resistance. Cable resistance depends on conductor material, cross-section, and length: R = (resistivity x length x 2) / cross-section (factor 2 for the return conductor). For copper at 20°C, resistivity is approximately 0.0175 ohm.mm2/m. A 20-metre 1.5 mm2 copper circuit at 10 A drops about 4.7 V on a 230 V supply, which is 2% and acceptable; on a 12 V DC circuit the same drop would be nearly 40% and unworkable.
AC vs DC
Mains electricity is AC because it can be stepped up and down with transformers, making long-distance transmission practical. The voltage alternates as a sine wave at 50 Hz (Europe, Asia, Australia) or 60 Hz (North America, parts of Asia). When a multimeter reads 230 V AC, it is reading the RMS value, which is the DC-equivalent heating value. The peak of a 230 V RMS sine wave is about 325 V.
DC flows in one direction at constant voltage. Batteries, USB ports, solar panels, and vehicle wiring are all DC. Electronic devices internally run on DC; their power adapters or built-in supplies convert AC mains to DC. This is why a laptop charger specifies an output like "19.5 V DC 3.3 A" while its input reads "100-240 V AC 50/60 Hz".
RMS matters when measuring AC voltage or current. A multimeter in AC mode displays RMS automatically. When a datasheet states a capacitor's voltage rating, it is a DC or peak rating, not RMS. A 400 V capacitor on a 230 V RMS mains circuit is appropriate because the peak is 325 V, well inside the 400 V limit.
Frequently Asked Questions
What is the difference between W and VA?
Watts (W) measure real power: the energy actually converted to heat, light, or mechanical work. Volt-amperes (VA) measure apparent power: the product of voltage and current as the supply sees it. For a purely resistive load like a toaster, W and VA are the same. For loads with reactive components (motors, switching power supplies, fluorescent ballasts), current and voltage are out of phase, so VA is higher than W. The ratio W/VA is the power factor. A 500 W computer PSU with PF 0.7 draws about 715 VA from the mains, which is why a UPS must be sized in VA, not just watts.
Why do smaller AWG numbers indicate thicker wire?
AWG (American Wire Gauge) is based on the number of drawing dies a wire passes through during manufacture. More draws produce thinner wire, so a higher AWG number means more draws and a thinner conductor. AWG 24 (0.51 mm diameter) is common for signal wiring; AWG 10 (2.59 mm) is used for 30 A household circuits. The scale runs from AWG 0000 (4/0, the thickest at 11.7 mm diameter) down to AWG 40 (0.08 mm). When comparing to metric cable sizes, AWG 14 is roughly 2.5 mm2 and AWG 12 is roughly 4 mm2.
What does RMS voltage mean on my multimeter?
RMS (root mean square) is the AC voltage value that delivers the same heating power as an equivalent DC voltage. For a perfect sine wave, RMS = peak voltage / 1.414. So 230 V RMS AC has a peak of about 325 V. Most basic multimeters assume a sine wave and calculate RMS from the peak. True-RMS multimeters measure the actual waveform shape, which matters for variable-speed drives, dimmers, and switch-mode supplies that produce non-sinusoidal waveforms. When you read a mains outlet and see 230 V, that is the RMS value; the actual voltage swings from +325 V to -325 V 50 times per second.
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