Volts, Watts, Ohms and Amps – What Are They And Why Do They Matter To Guitarists?

Were you paying attention in science class at school? We’re about to get a bit technical. You’ve probably read these terms in product manuals, even based purchases off them. But do you know what they actually mean?

Cian Hodge

Cian Hodge

Watts, volts, ohms, amps. It’s quite mind-boggling at first. Of course, you just want to ditch the science and make some music. But voltage, current and resistance apply to every electrical piece of gear in your arsenal, making them difficult to avoid for almost every guitarist.

For example, your guitar pedal requires 9v. Your guitar head produces 100w while the PA speaker it runs into has an 8Ω input. If you mismatch certain equipment, it could have a detrimental effect on tone and even damage your precious rig. Here are some electricity basics:

  • Voltage (V) is the electrical pressure between two points, measured in volts.
  • Current (I) is the flow rate, i.e the speed of electricity, measured in ampere, or amps.
  • Impedance/resistance (R) is the opposition to a flow of electricity, measured in ohms or with the omega symbol (Ω).
  • Wattage (W) is a unit of electrical power. This is calculated by V*I.


Wattage is the most obvious use of these scientific terms for a guitarist. This tells us how much power an amp has. The higher the watts, the harder a power amp can drive a speaker. Or if applied to a speaker in particular, how many watts a speaker can handle before it starts to clip the signal.

Although there’s an obvious correlation between watts and volume, the outcome also depends on variables such as valves and speaker type. In the mid-20th century, a speaker could only handle about 30w maximum. Roll forward a few decades and you’ve got guitar cabs that can comfortably deliver 100w or 150w for standard electric guitars. This provides more clean headroom at high volumes.



Take note of the ohmage when plugging a piece of musical equipment into a circuit. In an ideal world, you want to match output and input impedance to get the pure, intended sound of your gear. There are three groups of impedance in which gear can be classified. Low, high and ultra-high.

Microphones and DI boxes are low impedance, meaning the ideal next step in the circuit accepts low power. A PA mixer is designed to take these kinds of inputs.

Guitar pickups and effects pedals are high impedance, so need to be plugged into a preamp that can deal with 800 ohms and or more. Ultra-high impedance like bass guitars can require an input impedance of one million ohms/1 megohms.

Most speaker cabinets have flexible ohmage inputs, so you’re not limited to just the one amp. It’s not the end of the world if you turn up to a show with mismatched gear anyway. But a good rule of thumb is to not go above double the ohms from high to low, or a quarter from low to high impedance. Otherwise, you could heavily wear or permanently damage the tubes and transformers.



Volts are mentioned most often when referring to guitar pedals. Unlike impedance, the voltage of a PSU and pedal need to meet exact specifications – no ifs or buts. Ignore this and you’ll end up with a useless box of wires.

Most pedals require 9v. More uncommon voltages include 12v, 18v and 24v. A quality power supply will handle a selection of these. Simply match what it says in the manual or on the pedal. While you’re at it, double check what voltage your guitar amp requires, just so you know for future reference. The general figure to look for is 240v, but some are also multi-voltage.

Polarity is yet another parameter you’ll need to confirm is correct. + should go with +, – with -. If these don’t match, your pedal will either be permanently damaged or you’ll wonder why your amp isn’t making a sound.

The supplied current from a PSU, measured in ampere or amps, should exceed what it says on the pedal. Most need somewhere between 400 milliamps and 1mA. Meet all these requirements and you should have no issue creating a hum-free pedalboard and guitar rig.


If you enjoyed this read, check out more of our Learn blog posts!

Head over to the Andertons website to get yourself some new gear and show off everything you’ve learned.

Cian Hodge
Cian Hodge
Cian is a writer for the Andertons team. He shares his birthday with Muse frontman Matt Bellamy and believes he will one day reach the same level of stardom. Cian is a big metal fan so naturally loves Bare Knuckle pickups and pointy guitars.

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