This headphone amp power calculator answers a narrow electrical question: given a headphone’s published sensitivity and impedance, how much power, voltage and current does it take to reach a given sound pressure level, and how much more is needed to pass the peaks without clipping. Everything it produces follows from two definitions and Ohm’s law. There is no judgement in it about whether a headphone is hard to drive or whether an amplifier is good.
The reason it is worth calculating rather than guessing is that the two common sensitivity units point in opposite directions. A 300 ohm headphone and a 32 ohm headphone can have the same figure per milliwatt and wildly different figures per volt, and the voltage figure is the one that decides whether a phone or a laptop can drive them. Arb Digital built this page around that conversion because it is where nearly all the confusion lives.
What This Calculator Does
It computes the average power required for your target level, the peak power once your headroom allowance is added, and the RMS voltage and current at that peak. It converts your sensitivity figure into the other unit so you can compare specifications that were quoted differently. And if you enter the maximum unclipped output voltage of your own amplifier, it reports the level that amplifier reaches into this load and the margin either way.
It publishes no amplifier specifications and no headphone specifications. Both are properties of specific products, and a table of remembered figures is exactly how audio pages become wrong. The bar display shows what the same headphone needs at several target levels, which is the most useful thing here because power requirements rise tenfold for every 10 dB.
How to Use It
- Copy the sensitivity from the specification sheet and set the matching unit. Getting this wrong is the single biggest source of error.
- Enter the nominal impedance, remembering it is one figure standing in for a curve that varies with frequency.
- Set a target average level, not a peak. The headroom field handles the peaks separately.
- Set the headroom to match the material you listen to. Dynamic recordings need far more than compressed ones.
- Add your amplifier’s maximum output voltage if you know it, and read the margin rather than a verdict.
The Formulas and Where They Come From
Sensitivity quoted per milliwatt says how loud the headphone plays with one milliwatt into it. Because level in decibels is ten times the base-ten logarithm of a power ratio — the definition set out in the HyperPhysics note on decibels — the level at any other power follows directly:
SPL = SmW + 10 · log₁₀(P in mW), and rearranged, P = 10(SPL − S) / 10
Voltage and current then come from Ohm’s law applied to the power: V = √(P · Z) and I = V ÷ Z, with P in watts. Sensitivity quoted per volt uses the same logic on a voltage ratio rather than a power ratio, so the factor is twenty rather than ten: SPL = SV + 20 · log₁₀(V).
Converting between the two units needs the impedance, because one volt delivers a different power into a different load. One volt into Z ohms is 1000 ÷ Z milliwatts, so SV = SmW + 10 · log₁₀(1000 ÷ Z). This is the step that explains why high-impedance headphones need voltage and low-impedance ones need current.
Worked example with the defaults. A 300 ohm headphone rated 100 dB SPL/mW, targeting 110 dB average. The required power is 10(110 − 100)/10 = 10 milliwatts. That is 0.01 watts, so the voltage is √(0.01 × 300) = 1.732 V RMS, and the current is 1.732 ÷ 300 = 5.77 mA. Adding 12 dB of headroom multiplies the power by 101.2, giving 158.49 milliwatts peak, 6.895 V RMS and 22.98 mA. The same headphone’s sensitivity expressed per volt is 100 + 10 × log₁₀(1000 ÷ 300) = 105.23 dB SPL/V, which you can verify: one volt into 300 ohms is 3.333 mW, and 100 + 10 log₁₀(3.333) is the same 105.23.
Why Impedance Decides Which Number Matters
Look at the peak voltage figure above: 6.9 volts RMS from a 300 ohm headphone at a demanding target. Many portable outputs cannot produce that, which is the real reason high-impedance headphones sound thin from a phone. It is not that they need more power in absolute terms — the current is tiny, under 25 milliamps — it is that they need voltage swing the source cannot produce.
Run the same calculation at 32 ohms and the picture inverts. The voltage required drops by roughly the square root of the impedance ratio, so it becomes comfortably reachable, but the current rises by the same factor. A low-impedance planar with poor sensitivity can ask for hundreds of milliamps, and a source that runs out of current rather than voltage distorts in a different and usually uglier way.
This is why “hard to drive” is not one property. A headphone can be voltage-hungry, current-hungry, or simply insensitive, and the fix differs in each case. The Ohm’s law calculator and the electrical power calculator handle the underlying relations on their own, and the RMS voltage calculator is useful when a specification quotes peak rather than RMS.
Why 10 dB More Costs Ten Times the Power
Power scales logarithmically against level, so every 10 dB is a factor of ten in power and a factor of 3.16 in voltage. Going from 100 dB to 110 dB on the default headphone moves the requirement from 1 milliwatt to 10. Going to 120 dB would take 100 milliwatts, and that is before headroom.
Headroom compounds it. If your recording has 12 dB of crest factor, the amplifier has to be capable of nearly sixteen times the average power just to pass the peaks cleanly. Amplifiers that clip on transients while sounding fine on average material are extremely common, and this is the arithmetic behind it. The decibel calculator covers the ratio maths on its own.
Because the numbers climb so fast, it is worth stating what the levels mean. The joint ITU-T H.870 recommendation on safe listening devices, developed with the World Health Organization, frames safe listening as a weekly sound allowance equivalent to 80 dBA for 40 hours, with a lower allowance for children and sensitive users. Every 3 dB above that roughly halves the time the allowance permits. A 110 dB target is a measurement scenario, not a listening level.
What the Calculation Cannot See
Sensitivity is measured at one frequency under one standard condition, and different manufacturers do not always specify the same way. Two headphones honestly rated at the same figure can differ audibly in perceived loudness because of where their energy sits. Treat the number as a starting point for comparison rather than a precise prediction.
Impedance is a curve, not a number. Dynamic headphones often have a large resonance peak in the bass where impedance rises several times its nominal value, and multi-driver in-ears can swing wildly across the band. If your source has meaningful output impedance, that interaction changes the frequency response audibly, which is why a low output impedance is generally preferred. None of that appears anywhere in the calculation here.
And an amplifier’s rated output is usually specified into one particular load. A figure quoted into 32 ohms tells you little about the same amplifier into 300 ohms, because one may be voltage-limited and the other current-limited. Use the specification for your actual impedance, and if the manufacturer does not publish one, that absence is worth noticing.
Arb Digital builds calculators that name the formula, cite the source and publish no invented tables. Browse the library, or tell us what your audience keeps arguing about.
Browse Free Tools Talk To Arb DigitalCommon Mistakes to Avoid
- Mixing up the two sensitivity units. Per milliwatt and per volt differ by ten times the log of 1000 over the impedance, which is a large number at high impedance.
- Sizing an amplifier for the average level. Peaks are what clip. Whatever headroom your material has, the amplifier has to pass it.
- Assuming power is the only constraint. High impedance needs voltage, low impedance needs current, and a source can run out of either.
- Treating nominal impedance as flat. It is a single figure standing in for a curve, and on some designs the curve moves by a factor of several.
- Reading a high target level as a recommendation. These are electrical calculations. Sustained loud listening carries a hearing risk that no calculator offsets.
Related Free Tools From Arb Digital
Work the underlying relation with the Ohm’s law calculator, get power from voltage and current with the electrical power calculator, handle peak and RMS conversions with the RMS voltage calculator, work in ratios with the decibel calculator, convert between level units with the sound level converter, and move between milliwatts and dBm with the dBm to watts converter. Everything else is in the free online tools hub.
Frequently Asked Questions
Take the sensitivity in dB SPL per milliwatt, subtract it from your target level, divide by ten and raise ten to that power. A headphone rated 100 dB per milliwatt needs 10 milliwatts for 110 dB. Add your headroom allowance on top of that, because peaks are what an amplifier has to pass without clipping.
One measures loudness at a fixed power, the other at a fixed voltage, and converting between them needs the impedance. The relation is sensitivity per volt equals sensitivity per milliwatt plus ten times the logarithm of 1000 divided by the impedance. At 300 ohms that is about five decibels; at 32 ohms it is about fifteen.
Because they need voltage swing rather than current, and small portable outputs are usually voltage-limited. The current involved is tiny, often under 25 milliamps, but the several volts required at a demanding level are beyond many built-in outputs.
Whatever the crest factor of your material is. Dynamic classical and jazz recordings can have a large gap between average and peak, while heavily compressed pop has very little. Twelve decibels is a common working assumption, and it multiplies the power requirement by nearly sixteen.
Because the decibel is logarithmic in power: ten decibels is a factor of ten in power and a factor of about 3.16 in voltage. That is why the requirement climbs so steeply as you raise the target level, and why headroom is expensive.
No. It publishes no amplifier or headphone specifications at all, because both belong to specific products. If you enter your own amplifier’s maximum unclipped output voltage into this impedance, it will report the level that reaches and the margin, which is arithmetic rather than a recommendation.
No. It is one figure standing in for a curve that varies with frequency, and on some dynamic and multi-driver designs the variation is large. If your source has appreciable output impedance, that interaction audibly changes the frequency response, and none of it appears in this calculation.
It is a calculation scenario, not a recommendation. Safe listening guidance from the ITU and the World Health Organization frames a weekly allowance equivalent to 80 dBA over 40 hours, with the permitted time falling sharply as level rises. Treat high targets as headroom arithmetic rather than as a place to set the volume.
This page performs electrical calculations from figures you supply and makes no recommendation about equipment or listening levels. Sustained exposure to high sound levels can cause permanent hearing damage, and the targets entered here are chosen by the reader, not endorsed by this page. Use manufacturer specifications for your own headphones and amplifier, and treat published sensitivity and impedance figures as nominal.
