What Size Amp Do I Need For Different Sized Subs?

If you are an automobile user, you consider a lot of things for your car. And being passionate about it makes you even more sophisticated about its stuff. Subwoofers are something you must be concerned about. 

So, what size amp do I need for different sized subs?

The amp you need depends on the PMS rating and the impedance of the subs you have. You should get an amp that has 1.5-2x more wattage compared to the PMS rating of your sub. Depending on the amp, you could even use 4 subs with 1 amp. Just keep that simple 2x PMS formula in mind and you’ll be fine. 

This is actually a peek through to the actual part. We have covered it in-depth in the article. So, read along.

Get started now!

First Things First, Do I Need an Amp for My Subwoofer?

Yes, you do need an amp for your passive subwoofer. Your bass frequency will sound flat and the subwoofer will not produce a louder sound without one. However, you won’t need an external amp for your powered subwoofer. 

Typically, a powered subwoofer has an amp built inside the enclosure. Although, that comes at a hefty cost. As only premium subwoofers are powered. 

Here’s the thing –

An amp amplifies the sound of a subwoofer while eliminating any distortion. An average subwoofer cannot produce loud sounds or bass without distortion. A subwoofer amplifier quickly solves the issue. 

Now that we’ve established that you do need an amp for your subwoofer. So, let’s get to talking about the size. 

What is Amplifier Size?

Amplifier Size is the classification of amplifiers based on their wattage. The size range is around 1W to 150W. Typically, the higher the wattage, the more powerful the amp is. 

Since we’re already on the topic of power, let’s talk about how subwoofer size impacts it. 

After the brief, we also got a chart. Over there, you can find the compatible amp for the respective subs.

How Does Subwoofer Size Impact Power Requirement?

The power requirement of a subwoofer goes up with its size. A 6’ Subwoofer typically requires 300 watts of power. However, a 12’ subwoofer power requirement goes up to even 12000 Watts. 

That is because, the bigger the size, the more power the sub is capable of putting out. As a result, the power requirement generally goes up with the size. 

Subwoofer Size to Power Requirement Graph
Subwoofer Size to Power Requirement Graph

In simpler terms, the bigger a sub is, the more space it has. The greater space allows for greater amplification. The chart below explains how the power requirement rises as a result of the size. 

Just like how the size of a subwoofer impacts power requirement, the amperage impacts it too. For example, a sound digital amp might or might not work for just any sub. 

So, how many amps does a subwoofer use? 

Subwoofers use 4-5 amps and higher-end ones go up to 10 amps. The amperage of a subwoofer depends on the resistance (in ohms). Usually, subwoofers have resistances of 1,2,4,6, and 8 ohms. 

8 ohms is the most common impedance and 4 ohms is theoretically the best for amperage. 

What Size Amp for Different Subwoofer Sizes?

You have to select the amps depending on the wattage and impedance of your subwoofer. Subwoofers come in different sizes like 10 or 12 inches, which translates to different wattage and impedance. You’ll have to match the amps evenly with the subwoofer to get the best results. 

Now then, how do you know what size amplifier to get?

Usually, you should get an amp 1.5 to 2 times the RMS/continuous wattage rating of the subwoofer at the impedance load. Depending on the subwoofer, the result will be different if you calculate the right amp for your subwoofer. 

This calculation applies to almost all the amps. As long as you follow it, you can easily choose your amp no matter what sub you have.  

As an example, how would you calculate the right amp size for 12-inch sub?

Find the RMS rating of the 12-inch sub at different loads. Generally, that is from 150 watts to 1000 watts and sometimes even more. So, considering 150 watts at 4 ohms, you’ll need an amp that can handle 300 watts at 4-ohm load. 

Furthermore, you can use a number of subwoofers with 1 amp too. I have some words regarding that. 

Amp Size for 1 Subwoofer

Amp size for 1 subwoofer is generally 400W-6000W depending on the size you’re going for. 15000w amps exist too but they’re not practical and basically are redundant in most cases. 

Like I said before, amp size for 1 subwoofer is easily calculable. There aren’t any complications to it and you can use both SVC and DVC amps for it. 

SVC stands for Single Voice Coil whereas DVC stands for Double Voice Coil. Both are types of amps. DVC is more expensive and efficient compared to SVC. 

The size of a sub does affect the amp you’ll need. As a demonstration, I’ll calculate the amp size for 10-inch sub.

The amp size for a 10-inch sub is 800W-4800W at 2 or 4-ohm nominal impedance. The most common RMS rating range is 400w-2400w at 2 or 4-ohm load. So, double that for maximum effectiveness, it comes to 800w-4800w. 

So, you can see clearly how the size of the sub affected the size of the amp. The table contains the rest of the values, further emphasizing the effect of sub size on amp size. 

Subwoofer SizeAmp SizePrice
8 Inches400W-2400W at 2,4 ohmCheck Price from Amazon
10 Inches800W-4800W at 2,4 ohmCheck Price from Amazon
12 Inches1000w-5000w at 2,4 ohmCheck Price from Amazon
15 Inches1200w-6000w at 2,4 ohmCheck Price from Amazon

That concludes the amp size for 1 subwoofer. But, what about multiple subwoofers? Here’s an analysis of that. 

Amp Size for Multiple Subwoofers

Amp size will double with the number of subwoofers. Multiply the number of subwoofers with the PMS rating. Then double that number to get the correct amp size. 

Let’s start with adding only 1 sub to the mix, Can 1 amp power 2 subs?

Yes, 1 amp can power 2 subs. If 2 subs are of 300W pms rating, then a single 1200w amp will do the job. Both SVC and DVC amps can do it. However, You might require more amps when you get to the high-end subs. That would be more cost-effective and efficient. 

If you decide to go up to 3 subs, Can 1 amp power 3 subs?

1 Amp can power 3 subs, but DVC amps would be more efficient compared to SVC amps in this case. Furthermore, the impedance will be around 1.33ohm, you’ll have to adjust to a higher powered than needed 1-ohm amp to circumvent that. 

However, if you’re a little low on budget, you could go for single-channel amps. So, Can 1 amp single channel power 2 subs?

Technically, 1 single channel amp can power 2 subs. The efficiency will be lower and the subs won’t reach full potential in terms of sound. That’s because the amp won’t supply enough power. 

Here’s a table explaining the amp needed for each size when you’re getting two subs. 

Subwoofer SizeAmp Size (at 2,4 ohm) Check Price
2×8 Inches800W-4800W Check Price
2×10 Inches1600W-9600W Check Price
2×12 Inches2000w-10000w Check Price
2×15 Inches2400w-12000wCheck Price

The table incorporates all the sizes of a single amp for 2 subs. For example-

Kenwood 12” 2 subs need a 1600w amp at 4-ohm load. Kicker subs similarly require a 3200w amp at 4-ohm load. They all follow the basic PMS Rating calculation. Basically, double everything for the right powered amp. 

But If you’re looking for 12” subs yourself, nothing beats the MTX Audio Terminator Series. Furthermore, if you want more power in 12’, Skar offers a good choice too. 

Amp Size for 3 Subs

Things are a little different when it comes to 3 subs. So, what size amp do I need for 3 10 inch subs?

You need a 2400W-14400W DVC amp for 3 10 inch subs, at a 1.33ohm load. But 1.33 ohm load amps aren’t available. So, you have to compensate with a higher powered amp than what you need at 1 ohm. 

According to the forum I analyzed most of the people suggested Kicker CX1200.1 1200W Mono D Audio Amplifier if you have a 3 sub setup.

The higher power will balance with the 1.33ohm load to go down to the needed wattage. 

Furthermore, for 3 12 inch subs, you’ll similarly need a 3000W-15000W DVC amp at 1.33 ohm load. 

Here’s a guy who was 16 when he put an amp and three 12” subs in the trunk of the ‘78 Camaro.

Amp Size for 4 Subs

If you want even more subs, what size amp do i need for 4 8 inch subs?

You’ll need a 1600w-9600w 4-channel DVC amp at 2ohm load to run 4 8 inch subs. However, getting 2 10 inches sub will sound better while being more efficient than this setup. 

As you need a 4 channel subwoofer amp you should check the Skar Audio SKv2-4500.1D Competition Grade Subwoofer Amplifier.

Is Mismatched Subwoofer and Amp Size an Issue?

Yes, mismatched subwoofer and amp size is an issue when the amp is not as powerful. It will cause sound distortion. Furthermore, the bass will sound flat and the subwoofer will not be as loud as you’d want it to be. 

In general amps should be more powerful than subwoofers. But how much can you overpower a subwoofer?

You can overpower a sub upto 60watts to 100watts from its requirements. For examples, if your subs are 300 watts RMS combined, then you can go up to 360 watts RMS to be safe. 

So, does a more powerful amp make speakers sound better? 

Yes, a more powerful amp does make speakers and subs sound cleaner and louder. The best clarity and loudness come from amps that are twice as powerful as speakers and subs. 

Before finishing the topic, I should talk a little about impedance. A lot of people think that lower ohm is bad. So, Is 1 ohm bad for an amp?

No, 1 ohm is not bad for an amp if the amp is capable of running 1 ohm load. Conversely, Trying to run 1 ohm load on a lower capability amp will be bad. Match the nominal resistance to the capability of the amp and it will be fine. 


What factors to consider for the ideal sized amp for my subs?

You need to do a bit of calculation to find out this. First of all, reckon the watts RMS rating of your sub. Then find the product of sub ratings of each one and the quantity of the subs. And then you would be able to find out the total RMS rating. Then choose the amp that is within the range of this.

Will there be a problem using different amps for subs?

No, you can not use different amps for your subs without a valid measurement. But if you are planning to install 2 different amps for one sub, you can. However, you have to make sure that the requirements are met accordingly. Without following that, there would be problems.

Is it impossible to make amps greater than the subs?

Well, you can actually install amps greater than the subs if you want. But it is recommended not to do that so. Although it can be good at times like in passive sub, it is better not to do so. Because there could be a few internal issues that you might not be aware of.

Final Words

Now you got your answer, what size amp do I need for different sized subs! We believe you now have a detailed idea about their different sizes.

Make sure you ascertain the compatibility sizes prior to making the purchase. Because you would not like to waste your money on it.

Best of luck!

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