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Room Ratio Analyzer

This room ratio analyzer checks your room dimensions (length, width and height) against the ITU-R BS.1116 / IEC 268-13 ratio criterion and the Bolt area, flags near-integer ratios that pile modes up, and finds the nearest published preferred ratio — plotted on a Bolt chart.

ℹ Room ratios only predict how evenly the low-frequency room modes are spread — they say nothing about reflections, reverberation or treatment. A good ratio is a head start at the design stage, not a fix: a well-treated “bad” room can beat an untreated “good” one, and most people can’t change their room’s dimensions anyway. Use this when choosing or building a room. The criteria shown are real published references (Bolt 1946, ITU-R BS.1116, IEC 268-13, Sepmeyer 1965, Louden 1971). Units cancel, so any consistent unit works.

Bolt chart — mid-dimension/smallest (x) vs largest-dimension/smallest (y), normalised so the smallest dimension (usually the height) = 1. Green zone = ITU-R BS.1116 / IEC recommended region; cyan dots = published preferred ratios; green dot = your room.

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How It Works

Every room has standing waves (room modes) at frequencies set by the distance between parallel surfaces: roughly f = c/(2·distance) and its multiples. When two dimensions are equal or in a simple whole-number relationship, their modes land on the same frequencies and stack up, giving a big boom there and a gap elsewhere. The point of a good ratio is to spread those modal frequencies out as evenly as possible. This tool normalises your room to 1 : W/H : L/H (smallest side = 1) and tests it three ways: the ITU-R BS.1116 / IEC 268-13 inequality (1.1·x ≤ y ≤ 4.5·x − 4, with both ratios under 3); a check that no dimension ratio sits within 5% of a whole number; and the distance to a set of published preferred ratios (Sepmeyer 1965, Louden 1971, the golden ratio). The Bolt chart plots your room against the favourable region first mapped by Bolt in 1946.

Treat the result as design guidance, not a verdict on how the room will sound. Ratios only address the low-frequency mode distribution; they ignore reflections, reverberation time, and the fact that furniture and treatment change everything. Choosing good room proportions is most valuable at the studio design stage, before any construction is committed. If you’re building or choosing a room, aim inside the green zone and away from integer ratios. If you’re stuck with the room you have, don’t worry — bass trapping, speaker and seat positioning, and EQ address modal problems regardless of the ratio. For the exact mode frequencies, use the room mode calculator to see every axial, tangential, and oblique resonance; for a pass/fail on modal spacing, the Bonello Criterion Checker. If your ratio looks good but the room still sounds boomy, low reverberation time is often the missing fix — the RT60 calculator can show how much absorption you need.

Frequently Asked Questions

What’s wrong with a cube or a room with two equal dimensions?
Equal (or simple-integer) dimensions put multiple modes on the same frequencies, so the bass has a strong boom at those notes and holes between them. Spreading the dimensions out evens the response.
Is there one “best” ratio?
No. Several researchers (Sepmeyer, Louden, Bolt) published ratios that distribute modes well, and they disagree slightly — they form a favourable region, not a single magic number. Any ratio inside the recommended zone is fine.
My room is a “bad” ratio — is it ruined?
Not at all. Ratio only affects modal spacing. Bass traps, careful speaker/seat placement and EQ fix modal problems in almost any room — plenty of great-sounding rooms have unremarkable ratios.
Does the unit matter?
No. A ratio is dimensionless, so metres, feet or any consistent unit give the same result — just don’t mix units between the three boxes.
What is the Bolt area?
A region of length/height and width/height proportions, identified by R.H. Bolt in 1946, where small rooms tend to have a smooth low-frequency response. The green zone here is the closely-related ITU-R BS.1116 / IEC recommended region.
What does ITU-R BS.1116 say about room proportions?
ITU-R BS.1116 is an international standard for subjective assessment of small impairments in audio systems. It specifies that the listening room’s dimension ratios should satisfy 1.1·x ≤ y ≤ 4.5·x − 4 (where x = width/height and y = length/height, with both values under 3). This inequality defines the green region on the Bolt chart above. Rooms meeting this criterion tend to have acceptably even low-frequency mode distributions for critical listening.
What are Sepmeyer and Louden ratios?
Sepmeyer (1965) and Louden (1971) are researchers who published specific room dimension ratios known to distribute standing-wave frequencies smoothly. Sepmeyer identified several preferred ratios through computer analysis of modal density; Louden ranked a large set of ratios by a smoothness metric. Their ratios appear as cyan dots on the Bolt chart. They are reference points, not rules: any room within the favourable region is considered acceptable, not just rooms matching one of those exact values.
How do I use this tool when designing a home recording studio?
If you have flexibility over your room’s dimensions — building a dedicated studio, finishing a basement, or framing a new partition wall — use this tool at the planning stage to compare dimension options before anything is built. Aim for a ratio inside the green Bolt zone and avoid any two dimensions being within 5% of a whole-number multiple of each other. Once your ratio is confirmed, check the specific mode frequencies with the room mode calculator to identify any remaining problem frequencies and plan bass trap placement accordingly.
Does a good room ratio eliminate the need for acoustic treatment?
No. A good ratio spreads the low-frequency room modes more evenly, which is a meaningful advantage, but it does not eliminate them. Every enclosed rectangular room has standing waves; the ratio only controls how those resonances are distributed across frequencies. Bass traps, absorbers, diffusers, and careful speaker and listening-position placement are still necessary to achieve flat low-frequency response and controlled reverberation at any given listening position.

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