Work out the ohm load of your speaker wiring
This speaker impedance calculator gives the total load, in ohms, that a group of speakers presents to one amplifier channel when they are wired in series, in parallel or in series-parallel. It also handles dual-voice-coil subwoofers, speakers of different impedance, checks the result against the lowest load your amplifier is rated for, and estimates the watts each speaker gets.
Use it for home stereo, car audio and subwoofer builds, PA and guitar cabinets. A table lists every way your speakers can be wired, showing which hook-up keeps the amplifier safe and which gives the most power.
How to use the Speaker Impedance Calculator
- Enter the impedance printed on each speaker (for a dual-voice-coil sub, the impedance of one coil) and how many speakers share the channel.
- Choose Series, Parallel or Series-parallel; for series-parallel, say how many speakers are in each series string.
- Speakers of different impedance? Type them in the list box instead, for example 8, 4.
- Pick the lowest load your amplifier is stable into and, if you like, its power rating and the speakers’ power rating.
- Read the total load and the verdict, then check the table of other wiring options.
Speaker Impedance Calculator features
Series, parallel and series-parallel
Any number of identical speakers from 1 to 16, with a sketch of how the wires run.
Dual voice coils
Coils wired in parallel halve the impedance; in series they double it. Both options appear in the table.
Mixed impedances
Different speakers in series or parallel, with the power each one receives.
Amplifier check
Flags a load below the amplifier’s minimum and marks the safe option that gives the most power.
Watts per speaker
From the amplifier’s rating, using P = V² ÷ Z.
Series and parallel speaker formulas
Speakers behave like resistors for this purpose. In series (the + of one speaker to the − of the next) the impedances add: Z = Z₁ + Z₂ + …. Two 8 Ω speakers in series are 16 Ω. In parallel (all + terminals together, all − together) the reciprocals add: 1/Z = 1/Z₁ + 1/Z₂ + …, so n identical speakers give Z ÷ n — two 8 Ω speakers in parallel are 4 Ω.
Series-parallel combines both: build strings of speakers in series, then wire the strings in parallel. With identical speakers the load is Z × speakers per string ÷ number of strings, so four 8 Ω speakers as two strings of two come back to 8 Ω — a handy way to run four speakers from an amplifier that wants 8 Ω.
| Speakers | Series | Parallel | Series-parallel |
|---|---|---|---|
| 2 × 8 Ω | 16 Ω | 4 Ω | — |
| 2 × 4 Ω | 8 Ω | 2 Ω | — |
| 4 × 8 Ω | 32 Ω | 2 Ω | 8 Ω (2 strings of 2) |
| 4 × 4 Ω | 16 Ω | 1 Ω | 4 Ω (2 strings of 2) |
| 8 Ω + 4 Ω | 12 Ω | 2.67 Ω | — |
Is my amplifier safe at this load?
Every amplifier has a lowest impedance it is designed for — often 4 Ω for home receivers, 2 Ω or 1 Ω for subwoofer amplifiers. A load below that draws more current than the output stage is made for; the amplifier runs hot, distorts or shuts down. A load above the minimum is always safe but gives less power, because an amplifier that keeps its voltage delivers P = V² ÷ Z: double the impedance and the power halves.
The rating on a speaker is nominal. The international speaker standard IEC 60268-5 expects the impedance not to fall below 80 % of the rated value in the speaker’s working range, and the calculator shows that figure. Real speakers sometimes dip further, so leave a margin if your load is right at the amplifier’s limit.
Worked example: two dual-voice-coil subwoofers
Two subwoofers with dual 4 Ω coils can be wired three useful ways. Coils in parallel make each sub 2 Ω; two such subs in parallel are 1 Ω, and in series 4 Ω. Coils in series make each sub 8 Ω; two in parallel are 4 Ω and in series 16 Ω. On a mono amplifier stable to 1 Ω, the 1 Ω option gives the most power; on one stable only to 2 Ω, choose a 4 Ω option instead.
To see how loud the result will play, take the watts per speaker to the speaker wattage calculator. For general resistor maths, use the Ohm’s law calculator, and to size the enclosure the subwoofer box calculator.
Things to keep in mind
- Give every series-parallel string the same number of identical speakers, or they will not share power equally.
- Speakers of different impedance in parallel get different power: the lower-impedance one takes more. In series, the higher-impedance one takes more.
- Keep the polarity the same for every speaker, or the bass from one cancels the other.
- Bridged (mono) amplifiers see half the load each side; follow the maker’s minimum for bridged use, which is usually higher.
- Ceiling-speaker systems on 70 V or 100 V lines use transformers and are calculated by watt taps, not by impedance.
Speaker Impedance Calculator FAQ
What is the impedance of two 8 ohm speakers in parallel?
4 ohms. Identical speakers in parallel divide the impedance by their number, so two 8 Ω speakers give 8 ÷ 2 = 4 Ω. In series they would be 16 Ω.
How do I use this speaker impedance calculator for series-parallel wiring?
Choose Series-parallel, enter the total number of speakers and how many go in each series string. The calculator divides them into equal strings and wires the strings in parallel, then shows the load and a sketch.
Can I connect 4 ohm speakers to an 8 ohm amplifier?
Not one 4 Ω speaker per channel if the amplifier is only rated for 8 Ω. Two 4 Ω speakers in series make 8 Ω, which is safe. Many receivers have a 4 Ω setting — check the manual.
Is it better to wire speakers in series or parallel?
Neither is better in itself: choose the wiring whose load is at or just above your amplifier’s minimum, for the most power without overloading it.
How does a dual voice coil subwoofer change the ohms?
Each coil is a separate winding. Wire the two coils in parallel to halve the impedance (dual 4 Ω becomes 2 Ω) or in series to double it (8 Ω). Then combine the subs in series or parallel as usual.
Why does my amplifier get hot or cut out?
Usually the speaker load is below its minimum impedance. Raise the load by wiring more speakers in series.