Quick rule: about 10 watts RMS per person if there is going to be dancing, and half that for speech alone. Two hundred guests on a dance floor call for 1,500 to 3,000 W RMS spread across several points. Outdoors, add 30 % to 50 %. Below is the table by capacity and what changes with the space.
It is the question we get most often before a wedding or a village fiesta, and it usually arrives with a figure from an advert attached. These are the numbers we work with day to day in our sound for events service, so you neither come up short nor pay for power you will never use.
RMS watts and peak watts: do not be fooled by the figures
Before comparing equipment, work out which watts you are being quoted. RMS power is the real continuous power a speaker can deliver. Peak power, or the advertised PMPO figure, can double it, quadruple it or whatever the manufacturer fancies. Always compare in RMS. And bear in mind that perceived volume does not depend on watts alone: speaker sensitivity and sound pressure level, measured in decibels, matter just as much. Two 500 W RMS speakers can sound very different depending on their efficiency.
Indicative sound power by capacity
- Up to 50 people (small room, presentation, drinks reception): 300–600 W RMS with two powered speakers is usually more than enough.
- 50–100 people (country-house wedding, large hall): 600–1,200 W RMS, with a subwoofer if there is dancing.
- 100–300 people (marquee, wedding venue, private party): 1,500–3,000 W RMS spread across several points.
- 300–700 people (small square, warehouse, sports hall): 3,000–8,000 W RMS with subwoofers and, often, delay towers.
- 700–2,000 people (large street party, mid-size concert): 8,000–20,000 W RMS; by now we are talking about systems configured by an engineer.
- Over 2,000 people: a line array sized with acoustic prediction software, not with rules of thumb.
These figures assume music at party level. If the event is speech only (a ceremony, a rally, a presentation) you can roughly halve them: what matters is intelligibility, not punch. For the specific case of a ceremony, we set it out in our guide to sound for an outdoor wedding ceremony.
Why the same capacity demands more power outdoors
Indoors, walls and ceiling send part of the energy back, so less power carries further. The price you pay is fighting the reverberation. Outdoors there are no reflections: the sound disperses, and on top of that there is usually ambient noise and a local noise ordinance to respect. As a rule, an open-air event needs 30 % to 50 % more power than the same event in a room. And in very long spaces, more watts are not the answer: delay towers are, as we explain in how to put sound into a square for concerts.
Speech, background music or dancing? The content decides the watts
- Conferences and speeches: clarity of the voice comes first. Moderate power and good coverage.
- Background music at a reception or dinner: low levels, but spread across several points so that nobody has a speaker shouting in their ear.
- A dance set or mobile disco: subwoofers are non-negotiable here, and 40 % to 50 % of the power should go to the low end.
- Live music: add the power for the audience to the power for the stage monitors. A band needs considerably more system than a DJ for the same capacity.
“Better 4,000 watts well spread and well equalised than 8,000 piled into one corner. Even coverage always beats brute volume.”
How you can tell you have come up short
You do not notice it in the volume, you notice it in the quality. The system goes into limiting, the voice loses body and the kick drum stops landing even with the meters pinned. And at the back of the room people start talking louder, which is the most reliable sign of all: if the audience has to shout at each other, the sound is not reaching them.
Common mistakes when calculating sound power
- Comparing one system's peak watts against another's RMS watts.
- Putting in a single very powerful sound point: the people at the front suffer and the ones at the back cannot hear.
- Forgetting the subwoofer at events with dancing and making up for it by turning everything else up.
- Leaving no headroom. A system running at 100 % distorts and protects itself; the healthy place to sit is 60–70 %.
- Ignoring the available mains supply: watts also come out of the distribution board, and outdoors that is what has forced us to rethink a rig more often than anything else.
And what does the right sound system cost?
It depends on the system and on whether you need an engineer during the event, so be wary of fixed rates from anyone who has not seen the space. What can be said is that sizing it properly stops you overpaying. Give us the capacity, the type of event and a photo or a plan of the venue and we will propose the right system. Tell us about your case and ask for a quote with no obligation: we work across Spain with our own technical team, at private celebrations and at corporate events.