Enter your room dimensions to calculate its room modes, the reverberation time (RT60) and where to place your seat and speakers.
This free room acoustics calculator turns your room's length, width and height into the three numbers that decide how bass sounds in it. It works out the room modes (the frequencies where the room resonates), the RT60 reverberation time and the best seat and speaker placement, all in the browser and before you buy a single panel or move a speaker.
The three calculators, and the maths behind them
Room modes are standing waves between parallel walls. The axial ones follow f = 343 · n / (2 · L), where L is the distance between the two walls, so walls 5 m apart resonate near 34 Hz, 69 Hz, 103 Hz and so on. When several modes land on almost the same frequency they pile up into a boomy peak; where none land you get a dip. RT60 uses the Sabine formula, RT60 = 0.161 · V / A (V the volume in m³, A the total absorption in sabins), to estimate how long sound takes to fall by 60 dB. Placement puts your seat at 38% of the room length and the speakers in an equilateral triangle at ±30°, the stereo angle in ITU-R BS.775. It all assumes a rectangular, rigid box, so read it as a well-aimed starting point rather than a measurement.
How to use the calculator step by step
It takes a couple of minutes: type the three measurements and the calculator returns the modes, the RT60 and the placement. These are the steps.
- Measure the room in metres, wall to wall, and type the length, width and height. Use the real ceiling height, not a dropped one.
- Open Room modes and look for the clusters: two or more frequencies close together are the notes that will sound boomy and one-note.
- Switch to Reverb, pick how furnished the room is and compare the RT60 with the target for your use (table below).
- Open Placement and set the seat at 38% and the speakers in the triangle it draws; nudge the subwoofer to one of the suggested spots.
- Once the room is set up and you want the truth, furniture and leaks included, it's time to measure it with a microphone.
When calculating is enough, and when you should measure
Calculating is for planning and deciding: which room to pick, roughly how much treatment you'll need and where to sit. Because it starts from dimensions alone, it nails the modes and the placement but can't see what a real room adds, with its furniture, doors and leaks. That is what measuring is for, confirming the result and even revealing the peaks the maths doesn't anticipate.
What the room acoustics calculator is for
It mainly helps with five things: setting up a studio, picking a room, planning a home cinema, estimating treatment and placing the speakers. One at a time.
Setting up a home studio or mixing room
For mixing you want an even, dry sound, with an RT60 around 0.2–0.4 s and the modes spread out. Type your dimensions and watch the Schroeder frequency: below it (150–250 Hz in a domestic room) modes rule and you'll fight the bass; above it, absorption and diffusion take over. If two dimensions match or one is a whole multiple of another, expect trouble. Small mixing rooms, two to three metres a side, are the trickiest case.
Picking or ruling out a room by its dimensions
Before you commit a room, its ratio already hints at the result. A cube with three equal sides is the worst case, because the three axes resonate at the same frequencies and triple up. Whole-number ratios like 1 : 2 : 4 do much the same. Louden's and Sepmeyer's spread ratios distribute the modes, as the table and the figure show.
| Ratio | Verdict | Why |
|---|---|---|
| 1 : 1 : 1 (cube) | Avoid | All three axes resonate together: triple bass peaks. |
| 1 : 2 : 4 (multiples) | Avoid | Modes of one axis land on another's and reinforce. |
| 1 : 1.14 : 1.39 (Sepmeyer) | Good | Classic small-room ratio, modes well distributed. |
| 1 : 1.4 : 1.9 (Louden) | Best | Lowest modal overlap of the common ratios. |
| 1 : 1.6 : 2.33 (Sepmeyer) | Good | Works well in larger rooms. |
Setting up a home cinema
For cinema, aim for an RT60 of 0.2–0.4 s and an even surround field. Put the seat at 38%, the front left and right at ±30° and the centre between them; the calculator draws it to scale. If you're wiring a full surround layout, our guide on how to place the speakers of a 5.1 system covers the angles and heights for every channel.
Working out how much treatment your room needs
The RT60 tab tells you how far you are from target, and that distance decides how much absorption to buy. An untreated living room usually sits between 0.6 and 1.0 s; getting it down to 0.3–0.5 s takes real thickness on the first reflection points, not thin foam. For how many panels, how thick and where, see our guide on how much acoustic treatment a home cinema needs.
Placing the seat and the speakers
The 38% rule keeps you off the worst peaks and nulls of the length modes. From there, form an equilateral triangle with the two speakers, keep them at least 0.4 m off the walls and toe them in slightly toward your head. Corners load the bass, so a speaker jammed into one sounds heavy and uneven.
| Use | RT60 target | Note |
|---|---|---|
| Critical listening or mixing room | 0.2–0.4 s | EBU Tech 3276 for listening rooms, averaged 200 Hz–4 kHz. |
| Home cinema | 0.2–0.4 s | Clear dialogue and an even surround field. |
| Multi-purpose living room | 0.3–0.5 s | Livelier, still fine for films and music. |
| Untreated living room | 0.6–1.0 s | The usual starting point before adding absorption. |
Frequently asked questions
What are room modes?
Standing waves between parallel walls that make some bass notes much louder (peaks) and others almost disappear (nulls), depending on where you sit. They are the main reason a room sounds boomy or uneven in the bass.
What RT60 should I aim for?
For domestic listening, around 0.3–0.5 seconds and fairly even across frequencies. For critical listening or a studio, EBU Tech 3276 lowers the target to 0.2–0.4 s (averaged 200 Hz–4 kHz). Untreated living rooms are usually higher; very dead rooms can feel unnatural. RT60 here uses the Sabine formula and an average absorption.
Why sit at 38% of the room length?
That position tends to avoid the worst peaks and nulls of the main length modes, giving smoother bass. It is a well-known starting point — then fine-tune by ear or with measurements.
How accurate is this?
It is a guide. The maths assumes a rectangular room with rigid walls and uniform absorption; real rooms have doors, windows and furniture. Use it to understand and start, not as a substitute for measuring.
What room ratio is best?
Avoid a cube and whole-number ratios like 1 : 2 : 4, which stack the modes. Well-distributed ratios such as Louden's 1 : 1.4 : 1.9 or Sepmeyer's 1 : 1.14 : 1.39 spread them out. If you can't change the room, treatment and placement do the rest.
Does it work for a square room or a small bedroom?
Yes, mainly to diagnose: a square or cubic room is the worst case because the axes resonate together, and the calculator shows that pile-up clearly. You can't move the walls, so fix it with bass traps in the corners, the 38% seat and careful subwoofer placement.
What is the difference between axial, tangential and oblique modes?
Axial modes bounce between one pair of walls and carry the most energy; tangential ones (four surfaces) are about 3 dB weaker and oblique ones (all six) about 6 dB weaker. Axials cause most of the audible bass trouble, which is why the default view focuses on them.
Does this replace measuring the room with a microphone?
No. It predicts an ideal, empty room from its dimensions; it cannot see furniture, leaks or the real peaks. Use it to plan, then measure with a mic to confirm what your room actually does.