Speaker wattage calculator
Work out the power your speakers need
Enter your speakers' sensitivity, how far you sit and how loud you listen, and we'll tell you the watts per channel your amp should deliver (or whether your powered speaker gets there).
A 30 W per channel amp drives 90 dB speakers to peaks of about 100 dB at 8 feet, and 84 dB speakers only to about 94 dB. The power you need comes from six inputs, and this speaker wattage calculator asks for them one by one (sensitivity, distance, how many speakers play at once, average level, the music you play and the room). It returns the peak watts per channel, the watts you'll use on average and, if you enter yours, whether your amp keeps up.
It all runs in your browser with the free-field formula Crown publishes in its guide to sizing power amplifiers, and it shows you the math with your own numbers.
How to use the speaker wattage calculator
It takes a minute and you only need your speakers' spec sheet. These are the steps.
- Find the sensitivity on the spec sheet and enter it with its unit, and pick the impedance (8, 6 or 4 Ω). It matters when sensitivity is quoted at 2.83 V, because into 4 Ω those 2.83 V are 2 W and the real 1-watt figure is 3 dB lower, and it also sets how much the speaker wire loses. For a powered speaker, switch to powered mode and enter its max SPL instead.
- Enter the distance from your ears to the speakers in feet or meters (the unit selector sits next to the field), or tap your room size and the calculator fills in a typical distance (about 10 ft for a 270–320 sq ft living room, our own rule of thumb).
- Say how many speakers play at once. Two for stereo; one if you're sizing a single home-theater channel or a lone speaker, which takes twice the watts.
- Pick your usual average level. If you don't know it, measure it from your seat with the online sound level meter during a song you like.
- Pick what you play. Current pop and electronic music leaves less room between average and peaks than classical or movies, and that changes the watts up to tenfold.
- Decide whether to count the room and, if you already own an amp, enter its power per channel. You'll see the watts you need, the watts you'll use on average and how much headroom is left.
Where does the wattage figure come from?
It comes from subtracting speaker sensitivity from the peak level you want and adding the distance loss. A 90 dB speaker gives 90 dB at 1 meter with 1 W. At 2.5 m (about 8 ft) it loses 8 dB, which is 20·log10 of 2.5, and two speakers playing together add 3 dB. To play pop at an 85 dB average, with 95 dB peaks, you're short 95 − 90 + 8 − 3 = 10 dB, and 10 dB is ten times 1 W, about 10 W per channel. It's the same free-field calculation from Crown's guide.
Two rules fall out of it, and you can see both in the figure. Every 3 dB more of peak level, or 3 dB less sensitivity, doubles the watts. Every 10 dB multiplies them by ten. For the whole picture, with tables by room size and music we measured ourselves, read our guide on how many watts per channel your room really needs.
| Sensitivity (1 W/1 m) | Typical speaker | 95 dB peaks | 100 dB peaks | 105 dB peaks |
|---|---|---|---|---|
| 84 dB | Inefficient bookshelf | 57 W | 179 W | 567 W |
| 85 dB | Compact monitor | 45 W | 142 W | 450 W |
| 87 dB | Average living-room speaker | 28 W | 90 W | 284 W |
| 90 dB | Efficient tower | 14 W | 45 W | 142 W |
| 93 dB | High-sensitivity speaker | 7.1 W | 23 W | 71 W |
| 96 dB | Horn speaker or small PA | 3.6 W | 11 W | 36 W |
| 100 dB | Mid-size PA | 1.4 W | 4.5 W | 14 W |
What the result means
The big number is the power your amp must be able to deliver on peaks, per channel. The average one is what you'll use almost all the time, and it's usually 10 to 100 times smaller.
Peak watts and average watts
Music doesn't play at a constant level, so the amp spends most of its time far below its rating and only reaches for the watts on drum hits and big climaxes. How far the peaks sit above the average depends on the recording. We measured it with FFmpeg, as true peak minus integrated loudness (EBU R128), on four current, royalty-free pop and electronic tracks and on two public-domain recordings of the first movement of Beethoven's Fifth. The calculator's headroom options round those numbers up, because the average a sound level meter gives you also counts the quiet passages and leaves the peaks even higher. The table sums it up.
| What you play | Measured or reference headroom | Option | Peak watts vs. average |
|---|---|---|---|
| Current pop and electronic | 8.6–11.6 dB (4 tracks we measured) | +10 dB | ×10 |
| Rock, jazz, acoustic | 15 dB (our pick; Crown uses 15 dB in its home-stereo example and 10 dB for jazz and pop) | +15 dB | ×32 |
| Classical | 16.2–18.0 dB (2 recordings of Beethoven's Fifth) | +20 dB | ×100 |
| Movies | 20 dB (cinema reference, SMPTE RP 200, calibrated with pink noise at −20 dBFS) | +20 dB | ×100 |
Plenty, just enough or falling short
With your amp entered, the calculator works out the peak it reaches at your seat and compares it with the peak you want. With 3 dB or more to spare it says "Plenty of power", between 0 and 3 dB it says "Just enough", and below that "Falls short" (those thresholds are our own). Treat the verdict as a pointer, because it relies on the sensitivity on the spec sheet and on the amp's rated power, and not every brand measures them the same way.
Speaker wire takes its cut
A long, thin wire eats part of the power before it reaches the speaker. Enter its one-way length and gauge and the calculator adds that loss to the watts it asks for, and warns you when the wire takes more than 5% of the speaker's impedance, about 0.4 dB (our own threshold). With 8-ohm speakers, 16-gauge copper is good for about 50 feet; with 4-ohm speakers, half that. If you're running the wire along the baseboard or inside the wall, our guide on how to hide TV cables and home theater wiring has the full gauge table.
If you have a powered speaker
Powered speakers don't publish a sensitivity you can use here, because the amp is built in, but they do publish their max SPL at 1 m. Enter it in powered mode and the calculator subtracts the distance loss and adds the second box. A pair of boxes rated at 125 dB reaches peaks of about 112 dB at 6 m (20 ft), plenty for a party at a 95 dB average with pop. That figure is a ceiling, though. To find where your speaker actually starts to distort, measure its real clean level with the party test.
What the calculator can't know
It's an estimate, and every 3 dB of error in any input doubles or halves the watts. Sensitivity is an average across a frequency range and each brand measures it its own way. Inside a room the reflections add 3 to 6 dB (our estimate, based on the 6 dB Crown gives for a venue), which is why the "Leave it out (safe)" option asks for a bit more than you'll need. At high power a speaker heats up and compresses, so the last few dB cost more than the math says. And an amp's rating depends on how it was measured (the load, the frequency range, how many channels are driven and the distortion), so always compare the strictest figure on the spec sheet.
Frequently asked questions
What do I enter if the spec sheet has no sensitivity?
Try 87 dB, the average for a living-room speaker, and treat the result as a rough guide. For a powered speaker, use its max SPL in powered mode instead. If it publishes neither, the most reliable option is to measure its real clean level with your phone.
Where do I find my speaker's sensitivity?
On the manufacturer's spec sheet, usually as “Sensitivity (2.83 V/1 m)” in dB. For an 8-ohm speaker that is the same as 1 W at 1 m; for a 4-ohm one, 2.83 V means 2 W, so its true 1-watt figure is 3 dB lower. Most living-room speakers land between 84 and 90 dB.
What average level should I choose?
70 dB is background music you can talk over, 80 dB is normal listening, 85 dB is loud, 90 dB is very loud and 95 dB is party level (these steps are our own). If you're unsure, measure your usual level with a sound level meter from your seat and pick the closest step.
Which peak headroom should I pick?
It depends on what you play. The four current, royalty-free pop and electronic tracks we measured peaked 8.6 to 11.6 dB above their integrated loudness, so +10 dB fits them. Two public-domain recordings of Beethoven's Fifth measured 16.2 and 18.0 dB, and cinema sound is calibrated with 20 dB of headroom, so pick +20 dB for classical, movies and live recordings.
Why does “Leave it out (safe)” ask for more watts?
Because it assumes free field, as if you were outdoors. Inside a room, reflections add level. Crown estimates about 6 dB in a venue, and our own estimate for a furnished living room is 3 dB or more. Leaving it out is the safe choice, and every 3 dB of room help halves the watts.
Can I use an amp with more watts than the result?
Yes, and it's usually a good idea, because spare watts are headroom and a speaker is at more risk from an amp driven into clipping than from a bigger one used sensibly. Crown recommends amplifier power of 1.6 to 2.5 times the speaker's continuous rating for music, which leaves 3 to 6 dB of headroom for peaks.
Does it work for powered, PA or Bluetooth speakers?
Use powered mode. Enter the max SPL at 1 m from the spec sheet and the calculator tells you what peaks reach your seat. Passive PA boxes do publish a sensitivity, so they go in passive mode. Bluetooth speakers rarely publish either number, and their watts are not comparable across brands.
How much power does speaker wire lose?
Very little if it's thick and short. With 8-ohm speakers, 16-gauge copper wire loses about 0.4 dB over a 50-foot run, and 18 gauge loses the same in only 31 feet. With 4-ohm speakers those runs are cut in half, and copper-clad aluminum (CCA) wire behaves like copper two gauge numbers thinner (14-gauge CCA is about 16-gauge copper). Enter the length and gauge in the calculator and it adds the loss to the watts you need.
Does it work for a single home-theater channel?
Yes. Pick one speaker playing at once, the +20 dB headroom for classical and movies, and your average level. For cinema reference level (105 dB peaks per channel), 90 dB speakers at 11.5 ft (3.5 m) need about 390 W per channel in free field and about 100 W counting 6 dB of room help.