Convert jia (甲) to hectares. One jia is 2934 ping, or 0.9699 hectares — 3% short of a hectare, which is why land has two correct areas.

The formula

hectares = jia × 0.96991736

One 甲 is 2934 坪, and a ping is exactly 400/121 m², so:

1 甲 = 2934 × 400/121 m² = 9699.1735537… m²
1 hectare = 10,000 m²

A jia is not a hectare

It is 3% short, and that is the entire reason this page exists. The two units are close enough to be confused and far enough apart to matter over a real parcel of land:

	Square metres	Hectares	Ping	Acres
1 甲	9699.17	0.9699	2934	2.3969
1 hectare	10,000	1	3025	2.4711

A farm of 50 甲 is 48.5 hectares. Over a hundred 甲 the gap is three hectares — about 9000 ping.

Why land in Taiwan has two correct areas

Both units are in current use, for different purposes:

甲, 分 and 坪 appear in land deeds, in sale negotiations, and in how farmers and older landowners talk about a parcel.
Hectares and square metres appear in government agricultural statistics, in zoning documents, and in anything reported to an international body.

So the same field is 3 甲 on the deed and 2.91 hectares in the statistics, and neither number is wrong. Reports that convert one into the other without saying so are where the confusion starts.

The Taiwanese land units

Unit	Ping	Square metres	Hectares
坪	1	3.3058	0.00033
分	293.4	969.92	0.09699
甲	2934	9699.17	0.96992

Ten 分 make one 甲, which is the only round relationship in the set.

Quick reference

Jia	Hectares	Square metres	Acres
0.5 甲	0.485 ha	4850 m²	1.20 ac
1 甲	0.970 ha	9699 m²	2.40 ac
2 甲	1.940 ha	19,398 m²	4.79 ac
5 甲	4.850 ha	48,496 m²	11.98 ac
10 甲	9.699 ha	96,992 m²	23.97 ac
50 甲	48.496 ha	484,959 m²	119.84 ac
100 甲	96.992 ha	969,917 m²	239.69 ac

The mainland 畝 is a different unit again

A 市畝 is 666.67 m² — about 0.0667 hectares, and roughly one fourteenth of a 甲. Any Chinese-language source discussing land area needs checking for which system it is using, in exactly the way 台斤 and 市斤 do for weight.

Estimating in your head

Take off 3%. 20 甲 minus 0.6 is 19.4 hectares, which is the exact answer to one decimal place. Going the other way, add about 3.1%.

Jia (甲) to hectares