Digital feng shui luopan (compass). On mobile, uses device magnetometer for live bearing; on desktop, manual angle input. Shows 24 mountains + 8 trigrams + live sector readout. Cultural reference only.
Feng Shui Luopan Reader (风水罗盘)
Stand just inside the main door, facing out, with the phone flat and its top edge pointing the way you face.
Cultural reference only.
The 24 mountains are 15° each, with 子 centred on north (352.5°–7.5°), running clockwise in the order 程順則's navigators' manual 指南廣義 (1708) recites: 壬子癸丑艮寅甲卯乙辰巽巳丙午丁未坤申庚酉辛戌乾亥. The trigrams are in the Later Heaven arrangement (說卦: 坎 due north, 離 south, 震 east, 艮 north-east), 45° and three mountains each. A reading exactly on a line counts to the clockwise side.
The reading is a magnetic bearing, as a luopan's needle is: Apple documents iPhone's webkitCompassHeading as measured from magnetic north, and on other browsers only an absolute orientation event is used. A browser that offers only relative orientation cannot act as a compass, so the tool ignores it and switches to manual. No declination is applied; in Singapore it is about 0.24° east in 2026 (WMM2025).
How to use
Pick mode
On mobile: pick "📱 phone compass" (needs HTTPS + sensor permission). On desktop: pick "🖥️ Manual input" and drag the slider or type the degrees (negative or over-360 values wrap).
Stand in the doorway
Stand just inside the main door, facing out, phone flat with its top edge pointing the way you face. The reading is the door's facing (向).
Stay away from metal
Phone magnetometers are disturbed by iron, electronics and magnets. Best results outdoors or in an open room; if the reading jumps, calibrate with a figure-8.
Read sitting, facing and sector
The panel shows the magnetic bearing, "sitting X, facing Y", the mountain and trigram, and how many degrees the reading is from the nearest sector line. The closer to a line, the more it needs checking with a physical luopan.
Feng Shui Luopan: Placing a Bearing on the 24 Mountains
The luopan (罗盘) is the geomancer's magnetic compass, its concentric rings mapping one bearing onto several cycles at once. This tool draws two of them: the 24 mountains and the eight trigram directions. A physical luopan carries many more rings, and schools use them differently.
The 24 mountains
Each mountain is 15°, and 24 × 15° = 360°. The names are the twelve Earthly Branches, eight of the ten Heavenly Stems (戊 and 己 are absent) and the four corner trigrams 乾, 坤, 艮 and 巽. The early-Qing Ryukyu navigators' manual 指南廣義 sets them out most plainly: north 壬子癸, south 丙午丁, east 甲卯乙, west 庚酉辛, north-east 丑艮寅, south-west 未坤申, north-west 戌乾亥, south-east 辰巽巳 — three to each direction, the middle one centred on it.
"The practitioners rub a needle's point on a lodestone and it points south — yet always a little east of it, not true south." — Shen Kuo, 夢溪筆談 卷二十四 (方家以磁石磨針鋒則能指南然常微偏東不全南也)
Magnetic north and true north
A luopan's needle points to magnetic north, and so does a phone's compass, so both read a magnetic bearing. The difference from true north, the declination, varies by place and year. On the World Magnetic Model WMM2025 (British Geological Survey calculator, 19 October 2026) it is about 0.24° east in Singapore, 0.03° in Kuala Lumpur, 3.3° west in Hong Kong and 5.1° west in Taipei. In Singapore, magnetic and true north are less than a quarter of a degree apart.
What a phone compass can and cannot do
A phone magnetometer is pulled off by nearby metal, appliances and magnets, sometimes by several degrees. That is why the tool shows how far the reading is from the nearest sector line: close to a line, a small error moves you into the next mountain, and the reading should be checked with a physical luopan.
Sitting and facing
Facing (向) is the way the front of the house looks out; sitting (坐) is the way its back faces — 180° apart. 指南廣義's 正隅對向念法 lists the twelve opposite pairs: 子午, 卯酉, 寅申, 巳亥, 辰戌, 丑未, 坤艮, 乾巽, 甲庚, 壬丙, 乙辛 and 癸丁.
Shen Kuo saw the needle point a little east of south
Shen Kuo's 夢溪筆談 records that a needle rubbed on lodestone "points south, yet always a little east of it" — the needle does not point true north-south, which is what is now called magnetic declination.
Two of the ten Heavenly Stems, 戊 and 己, never appear on the ring: twelve branches, eight stems and four corner trigrams make exactly 24 names.
指南廣義 (1708) had navigators recite the ring clockwise from 壬: 壬子癸丑艮寅甲卯乙辰巽巳丙午丁未坤申庚酉辛戌乾亥.
子 straddles north, from 352.5° to 7.5° — so 355° and 5° are the same mountain, and 壬 begins at 337.5°, not 345° (345° is its centre).
The trigram ring is the Later Heaven arrangement of the 說卦 commentary: 坎 "the trigram of due north", 離 of the south, 震 the east, 艮 the north-east.
Each trigram spans 45° and holds three mountains, the middle one on its direction: 坎 is 壬子癸 with 子 due north; 艮 is 丑艮寅 with 艮 at 45°.
Sitting and facing are 180° apart: 坐子向午 sits north and faces south. 指南廣義 turns the twelve opposite pairs into a chant: 子午卯酉, 寅申巳亥, 辰戌丑未, 坤艮乾巽, 甲庚壬丙, 乙辛癸丁.
On WMM2025, declination in October 2026 is about 0.24° east in Singapore, 3.3° west in Hong Kong and 5.1° west in Taipei — the same reading sits more than twenty times further from true north in Taipei than in Singapore.
Apple documents webkitCompassHeading, the heading iPhone browsers report, as "measured in degrees relative to magnetic north" — so an iPhone reading is a magnetic bearing, like a luopan's.
The W3C orientation spec says relative orientation has an arbitrary reference frame — it tells you how far the phone turned, not which way it points. So this tool only uses absolute orientation.
Frequently Asked Questions
Common reasons: (1) orientation sensors need HTTPS (this site has it); (2) iOS asks for permission — a prompt appears; choose "Allow"; (3) some browsers offer only relative orientation, which cannot act as a compass, so the tool switches to manual mode; (4) desktop computers usually have no magnetometer — use manual mode.
Phone magnetometers are easily disturbed by metal, electronics and magnets: refrigerators, computers, speakers, magnetic phone-case clasps, cars, trains. Use it outdoors or in an open room after a figure-8 calibration.
Magnetic north, like a luopan's needle. Apple documents iPhone's webkitCompassHeading as relative to magnetic north, and the absolute orientation other phones report comes from the magnetometer too. No declination correction is applied. In Singapore declination is about 0.24° east (WMM2025, October 2026), small enough to ignore; Hong Kong is about 3.3° west and Taipei 5.1° west.
Two: the eight trigram directions outside and the 24 mountains inside. A physical luopan carries many more rings; this is an introductory reference.
No — this is a web tool. Everything runs in the browser: no download, no signup.
No. It shows only two rings, and a phone reading is easily disturbed. To fix a sitting and facing, check on site with a physical luopan — especially when the reading is close to a sector line.
No. The orientation sensor only reports rotation angles (α/β/γ) — not your location. Nothing is uploaded — all computation happens in your browser.
Yes, recommended. If the reading jumps, move the phone slowly in a figure-8 a few times so the magnetometer can re-settle on the local field. Recalibrate at a new location.
Each trigram has 3 mountains; the centre one is 子/午/卯/酉 or 艮/巽/坤/乾. The flanking ones use the other 8 branches (丑寅辰巳未申戌亥) and 8 of the 10 stems (甲乙丙丁庚辛壬癸 — no 戊 or 己). Branches, stems and trigram names together give 24 unique names.
Yes. All RECATOOLS tools are free (ad-supported). No signup, no paywall.
Method & sources
How it computes
Mountain = floor(((bearing + 7.5) mod 360) / 15) on the ring 子癸丑艮寅甲卯乙辰巽巳丙午丁未坤申庚酉辛戌乾亥 (子 centred on 0°); trigram = floor(((bearing + 22.5) mod 360) / 45), 後天 order 坎艮震巽離坤兌乾; sitting = bearing + 180°; plus the distance to the nearest sector line. Live heading: iOS webkitCompassHeading, else alpha from an absolute orientation event only (360 − alpha); magnetic, no declination applied (LuopanKernel).
What this tool implements
- 二十四山: 24 sectors of 15°, in the clockwise order 程順則《指南廣義》(1708) recites (二十四位順念法 「壬子癸丑艮寅甲卯乙辰巽巳丙午丁未坤申庚酉辛戌乾亥」), three to each direction with the middle one centred on it (定四正四隅之法 「北方壬子癸 … 東南辰巽巳」): 子 runs 352.5°–7.5°, 壬 337.5°–352.5°. A reading exactly on a line counts to the clockwise sector.
- 八卦: the 後天 placings of 易傳·說卦 (坎 正北, 離 南, 震 東, 艮 東北), 45° and three mountains each. 坐/向 are 180° apart; the twelve opposite pairs match 指南廣義's 正隅對向念法.
- Sensors: a heading is taken only from webkitCompassHeading (Apple: "relative to magnetic north"; refused when webkitCompassAccuracy is −1) or from an ABSOLUTE orientation event as 360 − alpha (W3C DeviceOrientation). A relative alpha — whose reference the spec calls arbitrary — is ignored, and the page switches to manual input if no heading arrives. Both sources are magnetic, as a luopan needle is; no declination is applied. WMM2025 declination on 2026-10-19: Singapore +0.24°, Kuala Lumpur +0.03°, Hong Kong −3.3°, Taipei −5.1°.
- Corrected 2026-10-19: the ring said to begin at 壬 on 345° (that is its centre; it begins at 337.5°); iOS webkitCompassHeading called a true-north heading (Apple: magnetic); "traditional feng shui uses true north" (a luopan reads magnetic); Hong Kong declination −2° (WMM2025: −3.3°); a relative orientation alpha shown as a heading; direction codes (N, NE …) printed in the Chinese readout; an unsourced pull-quote ("200 years before Europe"); 北宋《地理大成》, 36-layer, price, brand, Hall-effect and accuracy (±5-10°, ±1°, ±0.5°) claims; a Hong Kong "world's highest density" claim; 司南 "1,300/1,500 years" claims; a FAQ promising an automatic fallback the page did not make.
Sources
- 程順則《指南廣義》(福州, 康熙四十七年 1708), 二十四位順念法 / 定四正四隅之法 / 正隅對向念法, Wikisource: https://zh.wikisource.org/wiki/指南廣義
- 易傳·說卦 (後天八卦 directions), Wikisource: https://zh.wikisource.org/wiki/易傳/說卦
- 沈括《夢溪筆談》卷二十四 (「方家以磁石磨針鋒，則能指南，然常微偏東，不全南也」), Wikisource: https://zh.wikisource.org/wiki/夢溪筆談/卷24
- W3C. DeviceOrientation Event Specification, Candidate Recommendation Draft, 12 February 2025 (relative vs absolute orientation; compass heading = 360 − alpha): https://www.w3.org/TR/orientation-event/
- Apple Developer Documentation. DeviceOrientationEvent.webkitCompassHeading — "measured in degrees relative to magnetic north": https://developer.apple.com/documentation/webkitjs/deviceorientat…
- British Geological Survey. World Magnetic Model 2025 calculator web service, queried for 2026-10-19 (Singapore 1.3521°N 103.8198°E: declination +0.236°): https://geomag.bgs.ac.uk/web_service/GMModels/wmm/2025/
What can make this go out of date
- Browser sensor behaviour: DeviceOrientation needs HTTPS, iOS asks for permission, and whether a browser fires absolute orientation events varies; the page refuses relative ones rather than guessing.
- Magnetic declination drifts (Singapore about +1.9′ a year on WMM2025). No correction is applied, deliberately — the traditional instrument is magnetic — so the reading is never a true-north bearing.
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