VDC on a multimeter stands for Volts Direct Current. It’s the setting you use to measure the voltage of any DC power source, like batteries, car electrical systems, phone chargers, and circuit boards. On the dial, it’s typically represented by a V with a straight line and dashed line above it (⎓), distinguishing it from the wavy-line symbol used for AC voltage.
DC Voltage vs. AC Voltage
Your multimeter has two voltage settings because electricity comes in two forms. Direct current flows in one direction only, from positive to negative, at a steady voltage. Alternating current reverses direction many times per second, typically at 50 or 60 cycles per second, and its voltage fluctuates constantly. Wall outlets in your home deliver AC power. Batteries, USB ports, car cigarette lighters, and solar panels deliver DC power.
Using the wrong setting won’t damage your multimeter, but it will give you a meaningless reading. If you put the dial on VDC and touch the probes to an AC source, you’ll get a reading near zero or an erratic number. So knowing which type of electricity you’re measuring matters before you start.
Common Things You’d Measure on VDC
- Household batteries: AA, AAA, 9V, C, and D cells are all DC sources, typically ranging from 1.2V to 9V.
- Car batteries: A healthy car battery reads around 12.6V with the engine off.
- USB chargers and adapters: These convert AC wall power into 5V DC (or higher for fast charging).
- Laptop and desktop motherboards: Internal computer power supplies convert AC to DC, delivering 3.3V, 5V, and 12V to different components.
- Solar panels: These produce DC voltage that varies with sunlight intensity.
- Arduino, Raspberry Pi, and hobby electronics: Nearly all circuit boards run on DC.
How to Measure DC Voltage
Start by turning the dial to the DC voltage setting (⎓). Some multimeters also have a separate DC millivolt setting for very small voltages. If you’re unsure which to pick, start with the standard VDC position, which handles higher voltages.
Plug the black probe into the COM (common) jack. Plug the red probe into the jack labeled V (sometimes shared with the ohms symbol). Do not plug the red probe into the jack marked A, which is for current measurement and can blow a fuse or damage the meter if used for voltage.
Touch the black probe to the negative side of the circuit or battery and the red probe to the positive side. The voltage will appear on the display. That’s the full process.
If You Have a Manual-Ranging Meter
Older or less expensive multimeters require you to select a voltage range on the dial, such as 2V, 20V, 200V, or 600V. The rule is simple: choose the smallest range that’s still higher than the voltage you expect. For a 9V battery, you’d select the 20V range. If you have no idea what voltage to expect, start at the highest range and work downward. Starting too low won’t give you a meaningful reading, and some meters will flash “OL” (overload) to tell you the range is too small.
Auto-ranging multimeters skip this step entirely. They detect the voltage level and adjust automatically, which is why they’ve become the default for most users.
Reading the Display
The number on screen is the voltage in volts (or millivolts, if you’re on that setting). A fresh AA battery should read about 1.5V. A 9V battery fresh from the package will show close to 9.0V, dropping toward 7V or lower as it drains.
If you see a negative sign in front of the number, it means your probes are reversed: the red probe is touching the negative terminal and the black is on the positive. The voltage reading itself is still accurate, just with reversed polarity. You can either swap the probes or simply ignore the negative sign if you only care about the voltage level.
Safety Ratings to Know
Most DC measurements around the house involve low voltages, well under 50V, which pose little danger. But if you’re working with solar panel arrays, electric vehicles, or industrial DC systems, voltages can reach hundreds of volts. Your multimeter has a CAT (category) safety rating printed on it, and it matters in these situations.
CAT ratings range from I to IV, with each level designed for progressively more dangerous electrical environments. CAT I covers small electronic devices and low-energy circuits. CAT II covers single-phase household appliances. CAT III covers building distribution panels and large motors. CAT IV covers utility-level connections and outdoor conductors. Within each category, the meter is rated for a specific maximum working voltage, such as 300V or 600V. Never measure voltage that exceeds your meter’s rated category and voltage, because the real danger isn’t the steady voltage but the transient spikes that can occur in higher-energy systems.
For typical battery and electronics work, any multimeter’s VDC setting will handle the job safely. The CAT rating becomes critical when you move into automotive, solar, or building electrical work where DC voltages climb higher.