Question of the Day: How Many Watts Should My Amp Be?

This question of the day comes from Max in Stanhope, PA. He sent me an email asking about how many watts his amp should be. In his email he told me he was looking to get a new tube amp and was concerned about the wattage. He was savvy enough to be concerned about having an amp that was too loud and would not give him the sound he wanted.

Lets start with a brief definition of watts. The watt is a unit of energy and is named after the 18th century engineer James Watt. There is more technical information about power but lets keep it simple because we are talking about a tube guitar amp not the Space Shuttle..! The Watt is actually just a measure of power. The next part of the scenario we have to look at is the decibel. A decibel is actually two words, ‘deci’ (meaning one-tenth) and ‘bel’ (named after Alexander Graham Bell, the inventor of the telephone). A ‘bel’ is a unit of sound and a deci-bel is one-tenth of a bel…..(now you know)! The decibel is just a measure of loudness. So what do each of these have to do with the tube guitar amplifier?

From the above definitions watts and decibels are two different things. You can have a relatively low powered amp that is very loud and would be able to keep up with a drummer on a stage with no problem. Just because you have more watts does not always mean you are going to be louder and the watts increase is not directly proportional to the decibel increase. Take for example two Marshall heads. Let’s say one is rated for 50 watts and the other 100 watts. By looking at the watts you would think that the 100 watt head would be twice as loud because it has twice the power right? Wrong! The loudness difference between the 50 watt amp and the 100 watt amp is only 3 decibels (dB) which is not really a drastic difference. It would take 10 times the power of the 50 watt head to be twice as loud as the 100 watt head which is 500 watts! Ouch…..!

There is also the issue of speaker efficiency to consider as well. The efficiency of a speaker which is also called “sensitivity” is a measure of the speaker’s output (in decibels) with a specific amount of amplifier power (watts). Most often this is calculated by placing a microphone that is connected to a sound level meter at a distance of one meter away from the speaker. One watt of power is then sent to the speaker while the sound level meter measures the loudness in decibels. The output level results in a measure of efficiency. Another way to look at it is how efficiently does the speaker use the power. For example a speaker rated at 90dB will take twice the amplifier power to be the same volume as another speaker rated at 93 dB efficiency just like in our Marshall 50 watt vs 100 watt example. By the same token a speaker rated at 93dB will need ten times more power than a speaker with a 103 dB efficiency rating to be at the same volume. So you can now see how a relatively low powered amp with highly efficient speakers can be louder than a higher powered amp with much less efficient speakers. I’ve actually seen this situation a few times over the years.

That’s enough of the electronics textbook. Lets get back to our man Max. In a case like this with the question “how many watts should my amp be” you have to start by asking yourself…”What will the amp be used for”? Are you just going to play at home? Will you use the amp for some small clubs and rehearsal? Do you plan on playing a lot of outdoor events? The next question you should ask yourself is “Do I want the amp to sound perfectly clean or do I want it to break up a bit”? This opens up a bit of a can of worms because a Master Volume can tame a loud, high powered amp to sound overdriven at lower volumes. But lets say Max is looking at amps without a Master Volume so it will be easier to make a decision.

You do not need a very high powered amp for at home only use. The good ol’ Fender Champ which is rated at about 6 watts is perfect for home use. Just ask Jason Isadore at about them. Some of the newer low powered amps like the Blackheart’s are perfect for home jamming and some recording. Doing some club work will require some more power though. Get on a stage with a drummer and a few other instruments and you will need to step up the wattage into the 20-40 watt range. This will give you enough volume and punch for many situations. Obviously the 20 watt amp will probably break up a little sooner so if you like that sound that’s the way to go. The 40 watts will give you some more clean headroom and a clearer, cleaner tone. Playing outdoors can be challenging because your 20 watt amp that sounded unreal in the small to mid sized club could potentially sound like a popcorn fart outside. I know, I have been there and do not want to go there again. I had that experience once and now when I play outdoors I bring a pair of 45 watt 4×10 amps and I’m usually totally cool with that. You could afford to move up again to the 50-100 watt range if you are playing large venues and outdoors. Generally speaking a lower powered amp will have to be turned up louder to the volume necessary for a live gig but will be pushed into overdrive and not play too clean. Some players really like this and others do not. It is all subjective.

So there you have it Max. Ask yourself the two questions: “What will the amp be used for”? and “Do I want the amp to sound perfectly clean or do I want it to break up a bit”? Answering these two questions and going by the general guidelines I laid out should make it easier to choose the right amp for you. The next step would be to try the amps you are considering and see which one works for you. Thanks for hitting me up and I hope this helps. As always please feel free to ask me more questions if you have them…..I’m always happy to help!!


  • Living in a condo in Chicago, the Fender Champ is really the best option around. Tons of great tone at moderate volume. I’m sure my neighbors agree! Great write up Billy!

  • Thanks Jason!!!! Your blog ROCKS!!!!!!!

  • Please note the decibel is a logarithic scale (not a linear scale, where a doubling of intensity would double the value) measure, so a large range of values can be represented by a convenient number. This allows us to represent huge changes in sound level (from hearing a pin drop to stuffing our head inside a PA bin) in one scale. The human perception of sound is such that a doubling of actual intensity causes perceived intensity to always increase by the same amount. Because of the decibel’s logarithmic scale a doubling of power (or intensity) always causes an increase of approximately 3 dB, which corresponds to this human perception.

  • BDLH

    I think it’s the human male nature (or it is just guitarist nature?) to end up with an amp that bigger and louder than you need! I’d heard stories from older guitarist how their choice of amps has changed through the years, and they tend to get smaller.

    For gigging these days, PAs are so good, the smart thing to do is to mike your amp through a PA. Then all you need is to be able to hear yourself on stage. Typically, you’re using monitors or aiming your amp at yourself. Either way, you don’t need a huge amp.

    So I say, choose an amp for tone, not volume. A PA can make any amp sound huge.

  • ‘I’d heard stories from older guitarist how their choice of amps has changed through the years, and they tend to get smaller.’ BDLH

    Nowt to do with the power of the amp, BDLH, more to do with decreasing power of the lower back muscles as age marches relentlessly on. I’ve just waved goodbye to my Boogie mkIII Simul Class (best clean amp ever, trust me) before it finally crippled me. New rule, if I can’t lift it easily with one hand, it’s not the right amp. You never see sax players having to carry their own PA system around, so why do guitarists? Roy Buchanan, among many others, seemed to manage fine, so get an amp that makes you sounds good and let the sound engineer worry about it after that……. (period)

  • I agree. I have been using the ZT Lunchbox on gigs with really great results. You can’t get much smaller than that….. I dump a mic in front of it and it sounds great! -Billy

  • Steve

    BDLH has it absolutely right. I’ll add just a couple of more thoughts…

    Back when I started in rock bands (40 years ago), we didn’t have the great PA systems that are available today. Our amps did the talking (and I have the Tinnitus to prove it). Today you can sound great with a 50 watt amp that’s mic’ed through the PA.

    Please respect the elder you will one day become and wear hearing protection. You’ll thank yourself for wearing a good in-ear monitor cranked down.

    Amp manufacturers do build fake cabs (no wiring, speakers aren’t real, lighter weight) for touring shows. I don’t know how the average joe or josephine can get a hold of fakes, but they exist.

  • Voice of Reason

    If you’re playing out, the key is not how loud your amp is, because it will be miked into the PA system anyway- the issue is, how big is the band or house PA system. Nothing worse than watching talented young musicians play through an underpowered PA system. If it’s outside or a larger bar/cafe, it just sounds like crap. People start talking rather than listening to the music. The music should be loud enough that it engages the audience, and they can’t easily talk over it- so they listen.

    The best sounding amp I ever had, was a 1955 Fender Tremolux tube amp. It had tonal textures that no other amp has. Neil Young uses a similar amp mic’d into his massive PA system during the “Rust Never Sleep” “Live Rust” etc. tours. One amp mic’d in, that’s all you need.

    Back in the “old days” the rock groups used walls of Marshall amps because the PA was used mainly for vocals, drums, keyboards. Sometime during the 1970’s-early 80’s they started mic-ing everything through the PA and even using electronic drums to simulate the drums when the drummer hit a certain drum.

    It was a 2-edged sword, it sounded better in some ways, but live bands have lost some of their realism because the PA sound is becoming too processed and digital sounding.

    IMHO the peak of live sound was the mid-1970’s double live rock albums, after that it seemed to lose some tonal quality.

  • I agree….smaller amps mic’d through a proper PA. It just makes sense. Playing outdoors however I find that I need a more powerful amp because a little 15 watter with 10″ speaker seems to get lost. I also think that music in general has lost tonal quality because of the digital age. Another double edge sword……the editing flexibility of digital and auto tune vs the warm and musically sounding 2″ tape, analog etc…. -Billy

  • BluesPauly1980

    this might be a little late and off subject but…
    i heard that the reason them old Valco amps from the 40’s and 50’s break up so early is because the power tube only puts out half the power that the amp can handle….so if this is true can i change one of the tubes in my classic 30 to get that kind of sweet early break up that is so desirable for a blues lover like myself.

    (i hope this question makes sense to you Billy…or anyone else who can help on here ’cause i’m only getting started with all this technical stuff, changing tubes and what not.)

  • Hey BluesPauly- Thanks for visiting!!! Never too late my friend….not at all!

    I think what you are referring to is that the output tubes are running at a lower voltage than the actual tube is spec’d for. Generally speaking if you run output tubes at a lower voltage then the headroom of the amp will probably decrease as well as overall volume. This can be great to some, bad to others….

    In the case of your Classic 30 you may want to try to pulling out two of the EL84 tubes and selecting the next lower speaker impedance setting to keep the relationship between the primary and scondary of the output transformer in proportion to the load (speaker). This will cut your output power by about half and the amp will break up a bit sooner and not be quite as loud. If you do not have an output impedance switch or dedicated jacks for different impedances then I would try a power attenuator like a THD Hotplate or something.

    Let me know what you think..!