Amplifier power
Amplifier Power Chart by Room Size
Quick answer
A 250 seat sanctuary throwing about 45 feet to the back row needs roughly 473 watts per loudspeaker, or about 945 watts across two boxes, for a blended service at 88 dBA with 12 dB of peak headroom. A 500 seat room needs about 956 watts per box across three boxes.
Amplifier power is decided by three numbers, and seat count is only one of them: how far the furthest seat is from the loudspeaker, how sensitive that loudspeaker is, and how much peak headroom the service style needs. The formula is W = 10 ^ ((target + headroom - sensitivity + 20 log10(distance / 1 m)) / 10).
Every row below starts from a seat count, derives the room geometry from assembly planning practice at 7 to 8 square feet per seat, and works the power for a loudspeaker of 96 dB sensitivity, which is typical of a powered 12 inch cabinet. These are the same figures the amplifier power calculator produces and the same ones on the sanctuary size pages, so a number quoted in a meeting and a number printed by the tool cannot disagree.
On this page
How many watts does each size of sanctuary need?
For a blended service, which is piano and a small band at an 88 dBA average with 12 dB of peak headroom. This is the most common church target and the sensible default if you have not yet decided.
A 250 seat sanctuary needs about 473 watts per loudspeaker and roughly 945 watts in total, while a 1,000 seat room needs about 1,766 watts per box and 7,065 watts in total across four boxes.
| Seats | Room size | Throw to back row | Watts per box | Boxes | Total watts |
|---|---|---|---|---|---|
| 75 | 20 by 30 ft | 26 ft | 158 W | 2 | 316 W |
| 100 | 23 by 35 ft | 30 ft | 210 W | 2 | 420 W |
| 150 | 28 by 42 ft | 36 ft | 302 W | 2 | 605 W |
| 200 | 32 by 48 ft | 41 ft | 392 W | 2 | 785 W |
| 250 | 35 by 53 ft | 45 ft | 473 W | 2 | 945 W |
| 300 | 39 by 59 ft | 50 ft | 583 W | 3 | 1,750 W |
| 400 | 45 by 68 ft | 58 ft | 785 W | 3 | 2,355 W |
| 500 | 50 by 75 ft | 64 ft | 956 W | 3 | 2,868 W |
| 600 | 55 by 83 ft | 71 ft | 1,176 W | 3 | 3,529 W |
| 750 | 59 by 89 ft | 76 ft | 1,348 W | 4 | 5,392 W |
| 1,000 | 68 by 102 ft | 87 ft | 1,766 W | 4 | 7,065 W |
| 1,200 | 75 by 113 ft | 96 ft | 2,151 W | 4 | 8,603 W |
| 1,500 | 84 by 126 ft | 107 ft | 2,672 W | 4 | 10,687 W |
| 2,000 | 97 by 146 ft | 124 ft | 3,588 W | 4 | 14,353 W |
Room dimensions are derived from 8 square feet per seat below 150 seats, 7.5 up to 600 and 7 above that, in a room 1.5 times as long as it is wide. Throw is 85 percent of room length. Assumes a loudspeaker rated 96 dB sensitivity at one watt at one metre. Past roughly 600 seats the honest answer is usually a line array rather than more point-source boxes.
The same room at every service style
Service style changes the answer more than seat count does, because the target level and the headroom both move. This is one 250 seat room specified five ways.
The same 250 seat room needs 15 watts per box for speech and 2,368 watts for contemporary worship, a difference of more than 150 times from the same seat count.
| Service style | Target | Headroom | Watts per box | Total, 2 boxes |
|---|---|---|---|---|
| Speech and teaching only | 75 dBA | 10 dB | 15 W | 30 W |
| Traditional, hymns and organ | 82 dBA | 12 dB | 119 W | 237 W |
| Blended, piano and small band | 88 dBA | 12 dB | 473 W | 945 W |
| Contemporary worship band | 95 dBA | 12 dB | 2,368 W | 4,737 W |
| Modern, full band with in-ears | 100 dBA | 12 dB | 7,490 W | 14,979 W |
The headroom term is the whole ball game. Program material peaks 10 to 12 dB above its average, and an amplifier that only just reaches the average clips on every transient. Each of those figures is a factor of 10 or 16 in watts, which is why an 800 watt answer and a 100 watt answer can both be correct for the same room.
Why the same seat count gives two different answers
Three variables move the number, and understanding which one you are arguing about resolves most disagreements between quotes from different integrators.
Headroom. Speech runs 10 dB of peak headroom, music 12 dB. That two decibel difference alone is a factor of 1.6 in watts. Some suppliers quote continuous power at the average level with no headroom at all, which makes their number look attractive and their system clip on every snare hit.
Sensitivity. A 99 dB loudspeaker needs roughly one eighth the amplifier power of a 90 dB one at the same level and distance. This single specification moves the answer more than the room does, and almost nobody compares it. See the speaker sensitivity chart.
Distance. Power rises with the square of the throw, so doubling the distance to the back row quadruples the requirement. A long narrow room is far more expensive to serve than a wide shallow one with the same seat count, which is why the room dimensions column above matters as much as the seat count.
How to turn these watts into an amplifier you can buy
- Start from the furthest seat, not the seat count. Measure the actual distance from where the loudspeaker will hang to the back row. If your room is not the proportion assumed here, your own measurement wins.
- Find the sensitivity of the loudspeaker you intend to buy. It is on every specification sheet as dB at one watt at one metre. Substitute it for the 96 dB assumed above, remembering that every 3 dB halves the power needed.
- Pick the target level and headroom for your service style. 75 dBA and 10 dB for speech, 88 dBA and 12 dB for a blended service, 95 dBA and 12 dB for contemporary worship.
- Size the amplifier at 1.6 to 2 times the loudspeaker continuous rating. This is what every manufacturer application guide says. Under-powering blows more drivers than over-powering, because a clipped small amplifier sends sustained near-DC into a tweeter.
- Round up to a size that is actually sold. Amplifiers come in steps. There is no 473 watt amplifier, so a 250 seat room buys a 500 watt per channel model and runs it comfortably.
- Check the circuit before you order. Work the rack power draw with the power draw calculator. Amplifiers draw far less than their rated output on programme material, but the check is free and a tripped breaker mid-service is not.
Where this chart does not apply
The room geometry is a model, not your building. Seat count is converted to dimensions using assembly planning averages. A long narrow sanctuary, a fan-shaped room, a balcony or a transept will all differ. Where you have a tape measure, use it, and take the throw distance from the real loudspeaker position to the real back row.
It ignores the room acoustically. These figures are free field. A reverberant room actually reaches a given level more easily, because reflected energy adds to direct energy, but the intelligibility is worse. Power is never the fix for a reverberant room. See the RT60 target chart.
It assumes one loudspeaker covers its share of the room. Under-balcony seats, transepts and rooms deeper than about 80 feet need delayed fills, which are additional amplifier channels not counted here. See under balcony delay speakers.
Subwoofers are not included. The figures size the main loudspeakers for the target level. A contemporary or modern service also needs subwoofer amplification, typically as much again.
Past about 600 seats, point sources stop being the right tool. The chart keeps computing, but a four box point-source system in a 1,500 seat room cannot keep the front and back rows within a few decibels of each other. At that size the answer is a line array, and the power is distributed differently across the elements.
Sources
- Amplifier power formula and service style targets as implemented in this site’s amplifier power calculator
- Loudspeaker manufacturer application guidance recommending amplifiers rated 1.6 to 2 times continuous program power
- Assembly occupancy space planning figures of 7 to 8 square feet per seat in fixed seating
Frequently asked questions
How many watts do I need for a 250 seat church?
About 473 watts per loudspeaker, or roughly 945 watts total across two boxes, for a blended service at 88 dBA with 12 dB of peak headroom and a 96 dB sensitivity cabinet throwing 45 feet. A speech-only service in the same room needs about 15 watts per box, and a contemporary band service about 2,368, which is why the service style has to be settled first.
Why do amplifier recommendations vary so wildly for the same room?
Because three assumptions move the answer enormously and are rarely stated. Peak headroom of 10 against 12 dB is a factor of 1.6. Loudspeaker sensitivity of 90 against 99 dB is a factor of eight. And throw distance enters as a square, so doubling it quadruples the power. Two honest quotes can differ by a factor of fifty if they assume different values for all three.
Is it better to over-power or under-power a loudspeaker?
Over-power, within reason. Every major manufacturer application guide recommends an amplifier rated 1.6 to 2 times the loudspeaker continuous rating. Under-powering destroys more drivers than over-powering does, because a small amplifier driven into clipping sends sustained near-DC and heavy high frequency energy into a tweeter that was never designed to dissipate it.
Does a bigger amplifier make the system louder?
Only by 3 dB per doubling, which is just noticeably louder. Going from 500 to 1,000 watts is a barely perceptible change, and reaching twice the perceived loudness needs ten times the power. Choosing a loudspeaker with 9 dB more sensitivity delivers the same result as an eightfold power increase and costs nothing extra to run.
Do I need a separate amplifier if I buy powered speakers?
No. A powered loudspeaker has the amplifier and processing built into the cabinet, matched to the drivers at the factory, so the watts in this chart are simply a specification to compare against. What powered boxes need instead is mains power at every loudspeaker position, which in an installed system with flown boxes is often the harder problem.
How much power does a 1,000 seat church need?
About 1,766 watts per loudspeaker and 7,065 watts total across four boxes for a blended service, assuming 96 dB cabinets and an 87 foot throw. At that size the more important question is whether point-source boxes are the right approach at all, because a line array will hold the level far more evenly between the front and back rows.
Researched, not professional advice. This page is compiled from published manufacturer specifications, operator manuals, FCC rules, published standards and owner-review consensus, not hands-on testing. Sound system design, rigging loudspeakers overhead, and any electrical work are jobs for a qualified professional: have flown loudspeakers and their attachment points signed off by a structural engineer or a certified rigger, and have all wiring done by a licensed electrician to your local code. Wireless microphone rules change, so confirm the current FCC position before buying. As an Amazon Associate we earn from qualifying purchases.