How to Read the Readings on a Multimeter

For non-experts, the symbols on a multimeter can appear to be in a foreign language. However, even individuals with experience in electronics might sometimes need help when faced with a multimeter that uses unconventional abbreviations. Fortunately, understanding the settings and knowing how to read the scale doesn’t take long, so you can quickly get acquainted and start working.

Checking Alternating Current (AC) or Direct Current (DC) Voltage. Generally, V represents voltage. When accompanied by a tilde-like curve, it indicates alternating current (in household circuits), while a straight line or a dash represents direct current (mostly in batteries). The curve or straight line may appear next to or above the V symbol.

• Most household circuits use AC, but some devices may convert the power into DC through semiconductor components (like transistors), so always check the voltage symbol before testing an item.
• The setting for measuring AC voltage is usually marked as V~, ACV, or VAC.
• For testing DC voltage in a circuit, set the multimeter to V–, V---, DCV, or VDC.

Set the multimeter to measure current. The unit for measuring current is ampere, abbreviated as A. Depending on the circuit you need to check, select either direct current or alternating current. Analog multimeters typically lack the ability to measure current.

• A~, ACA, and AAC represent alternating current.
• A–, A---, DCA, and ADC denote direct current.

Identify the resistance measurement setting. The resistance measurement mode is usually denoted by the Greek letter omega: Ω. This is the unit for measuring resistance, also called ohms. On older multimeter models, this setting might be represented by the letter R.

Use DC+ and DC-. If your multimeter has this setting, switch to DC+ mode when testing direct current. If the screen doesn't display any readings and you suspect that you've connected the probes incorrectly, switch to DC- mode to correct it without having to change the wiring.

Understand additional symbols. If you're unsure why there are multiple settings for voltage, current, or resistance, refer to the troubleshooting section for more information on ranges. In addition to these basic settings, many multimeters include extra features. If multiple symbols are marked on the same setting, the multimeter may be performing two functions simultaneously, or you may need to consult the manual.

• ))) or a series of parallel arcs indicate the "continuity test" setting. When in this mode, the multimeter will emit a beeping sound when the probes are connected electrically.
• An arrow pointing right with a cross through it is the "diode testing" symbol, used to check whether a DC circuit is connected.
• Hz stands for Hertz, the unit for measuring AC frequency.
• The symbol –|(– represents capacitance measurement.

Read the labels on the ports. Most multimeters have three ports or holes, which are sometimes labeled with symbols as described above. If the symbols aren't clear, refer to the following guidelines:

• Always connect the black probe to the COM port (also known as the ground port), while the red probe connects to the negative terminal.
• When measuring voltage or resistance, the red probe should be plugged into the port labeled with the smallest current symbol (usually mA or milliamp).
• When measuring current, the red probe must be plugged into the port that supports the expected current value. Typically, the low-current port is fused and rated for up to 200mA, while the high-current port can handle up to 10A.

Correctly determine the scale on the analog multimeter dial. The analog multimeter has a needle positioned behind the glass face, which moves to indicate the result. Usually, three arcs are printed on the dial behind the needle. These are three distinct scales used for different purposes:

• The Ω scale is used to measure resistance, typically the largest arc positioned at the top. On this scale, the value 0 is on the right side, unlike the other scales which have 0 on the left.
• The "DC" scale represents direct current voltage.
• The "AC" scale represents alternating current voltage.
• The "dB" scale is the least used. A brief description of the "dB" scale is provided at the end of this section.

Record the voltage scale value based on its range. Carefully observe the DC or AC voltage scale. You will notice several numbers located beneath the scale. Check the range you have selected on the multimeter dial (e.g., 10V) and find the corresponding symbol next to one of these numbers. This is the value you will read for the result.

Estimate the value between numbers. The voltage scale on the analog multimeter functions similarly to a traditional ruler. Meanwhile, the resistance scale is based on a logarithmic system, meaning the same distance represents different value changes depending on where the needle is pointing. The spaces between numbers represent evenly divided segments. For example, if three spaces exist between "50" and "70", the corresponding values are 55, 60, and 65, regardless of whether the segments are evenly spaced.

Multiply the resistance value on the analog multimeter dial. Look at the range setting you have selected on the multimeter dial. This will be the multiplier for the result reading. For instance, if the multimeter is set to R x 100 and the needle points to 50 ohms, the actual resistance of the circuit is: 100 x 50 = 5000 ohms.

Learn more about the dB scale. The term "dB" or decibel is often the smallest scale found at the bottom of a multimeter’s needle display. This scale is logarithmic and measures the ratio of voltage (also called voltage increase or decrease). In the standard dBv scale used in the United States, 0 dBv equals 0.775 V measured at a resistance of 600 Ω. There are also other scales like dBu, dBm, and even dBV (with a capital V). To use the "dB" scale, you need to have a deeper understanding of the concept.

Set the range. Unless you have an auto-ranging multimeter, each basic mode (voltage, resistance, and current) comes with additional settings. This is the range you need to choose before connecting the probes to the circuit. To proceed, estimate a value slightly higher than the closest expected reading. For example, if you anticipate a reading of about 12 V, select the 25V range rather than the 10V range (assuming these are the two closest options).

• If you are unsure about the expected reading, always choose the highest range for the first attempt to avoid damaging the multimeter.
• Other modes rarely damage the multimeter, but it is advisable to default to the lowest resistance level and the 10V range.

Adjust when the reading shows "out of range". On a digital multimeter, the display will show "OL", "OVER", or "overload", indicating the need to select a higher range. Conversely, readings close to zero mean a lower range is more accurate. On an analog multimeter, if the needle remains still, reduce the range. If the needle jumps to the highest level, immediately switch to a higher range.

Disconnect the power source before measuring resistance. Turn off the switch or remove the battery supplying power to the circuit to obtain an accurate resistance measurement. When measuring resistance, the multimeter sends a current through the circuit, so if another current is running through the circuit, the reading will be incorrect.

Measure current in a series circuit. To measure the current, the multimeter must be connected "in series" within the circuit along with its other components. For instance, you can disconnect the positive terminal of the battery and connect one probe to it, with the other probe linking back to the battery to complete the circuit.

Measure voltage in a parallel circuit. Voltage is the variation in electrical energy across certain points in the circuit. The multimeter must be connected "in parallel" by attaching the two probes to two different open points on a closed circuit that has current flowing through it. This measurement must be done carefully to avoid inaccuracies.

Calibrate the ohm scale on a needle-type multimeter. Needle-type multimeters typically feature an additional dial marked with the Ω symbol for calibrating the resistance scale. Before measuring resistance, briefly touch the two probes together. Then, adjust the multimeter’s dial until the ohm scale reads 0. Once this is done, you can start your measurement.

• If the needle on an analog meter points below 0 even when the multimeter is on the lowest range, the "+" and "-" probes might be reversed. Swap the probes and try measuring again.
• If the analog meter face reflects light, tilt the multimeter left or right so the needle blocks the reflection, making it easier to read the measurement.
• If you are having trouble reading a digital multimeter, refer to the manual. By default, the device shows results as numbers, but sometimes it can display bar graphs or other formats.
• When measuring AC voltage, the reading may initially fluctuate and will stabilize to the correct value.
• If the multimeter isn't working, you should check the device itself to pinpoint the issue.
• If you struggle with remembering the difference between voltage and current, picture a water pipe. Voltage is the pressure of water moving through the pipe, while current is the pipe’s size. The pipe’s size determines how much water can flow through at any given moment.

• If the range you select is lower than the expected output rating of the circuit or battery, the multimeter may be damaged. Analog multimeters are generally more fragile than digital types, but the auto-ranging ones are the most durable.