Convert ping (坪) to square metres. One ping is exactly 400/121 m², or 3.3058 m², with a table of Taiwanese apartment sizes.

The formula

square metres = ping × 3.3057851

The factor is exact, and it is a fraction rather than a decimal:

1 坪 = 400/121 m² = 3.30578512396694… m²

To go the other way, multiply by exactly 0.3025. See square metres to ping.

Where 400/121 comes from

A ping is six Taiwanese feet square. The 台尺 is the Japanese shaku, defined as exactly 10/33 of a metre and carried into Taiwan during the colonial period, so:

6 台尺 = 60/33 m = 20/11 m
(20/11)² = 400/121 m²

Nothing here is measured or rounded. The unit is a definition built on another definition, which is why its reciprocal — 0.3025 — comes out exact too.

Quick reference

Ping	Square metres	Square feet
1 坪	3.31 m²	35.58 ft²
5 坪	16.53 m²	177.92 ft²
10 坪	33.06 m²	355.83 ft²
15 坪	49.59 m²	533.75 ft²
20 坪	66.12 m²	711.66 ft²
25 坪	82.64 m²	889.58 ft²
30 坪	99.17 m²	1067.50 ft²
40 坪	132.23 m²	1423.33 ft²
50 坪	165.29 m²	1779.16 ft²

Taiwanese property sizes

Every home in Taiwan is advertised, taxed and registered in ping. These are the sizes that actually appear:

Ping	Square metres	Typically
8–12 坪	26–40 m²	studio (套房)
15–20 坪	50–66 m²	one bedroom
25–30 坪	83–99 m²	two to three bedrooms
35–45 坪	116–149 m²	family apartment
50+ 坪	165+ m²	large apartment or townhouse

The number on the deed is not the floor you walk on

A Taiwanese listing quotes the 權狀坪數 — the registered area — which includes the main building, attached structures like balconies, and a share of the common areas: lobbies, stairs, lift shafts, plant rooms, sometimes a gym.

That share is the 公設比, and it is routinely 30% or more in newer buildings:

Registered	公設比 25%	公設比 32%	公設比 38%
30 坪	22.5 坪	20.4 坪	18.6 坪
40 坪	30.0 坪	27.2 坪	24.8 坪
50 坪	37.5 坪	34.0 坪	31.0 坪

A “40 ping” apartment in a modern block can be under 28 ping of usable interior — 92 m² rather than 132 m². Converting the number is the easy part; knowing which number you were given is not.

Hong Kong has the same problem in different words, as gross versus saleable area. See square feet to square metres.

Unit	Ping	Square metres
坪	1	3.3058
分	293.4	969.92
甲	2934	9699.17
Hectare	3025	10,000

A hectare is exactly 3025 ping, with no remainder — another consequence of the 400/121 definition. See jia to hectares.

Estimating in your head

Multiply by 3 and add a third of that. 30 ping × 3 is 90, plus 9 is 99 m² — the true answer is 99.17. For a rougher figure, ping × 3.3 is within 0.2%.

Ping (坪) to square metres