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How do I measure the area of a rice paddy field with my phone?

Tap the four corners of the paddy on the Satellite map with Measure > Measure Area, and the panel gives the area in m² or hectares. A 30 m by 100 m paddy reads 3,003 m² (0.3 ha); LandMeasure has no tan or se unit, so dividing by 991.7 gives 3.03 tan.

4 min read · Updated 2026-09-07

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Take one block of the kind you see all over consolidated rice land: a plain rectangle, roughly 30 m across and 100 m long, levees on all four sides. Four taps on the satellite view, zoomed in so each corner of the levee is big on screen.

The panel read Area 3,003 m², Perimeter 260.1 m, Points 4. The sides came to 30.02 m and 100.03 m.

One limitation worth noting: the units list in Settings > Units has Square Meters (m²), Hectares (ha), Acres (ac) and four others, but no tan, se or tsubo. If you think in those, you do one division yourself. Here it is, done once with the exact factors.

The 3,003 m² paddy in other units (tan, se, are and tsubo are computed outside the app)
UnitFactorThis paddy
m² (in the app)3,003 m²
ha (in the app)10,000 m²0.3 ha
are (a)100 m²30.03 a
tan300 tsubo = 991.7 m²3.03 tan
se30 tsubo = 99.17 m²30.3 se
tsubo3.3058 m²908 tsubo

Keep the app on Square Meters (m²) for paddies. Hectares (ha) rounds to two decimals, so a 0.1 ha paddy and a 0.104 ha paddy look the same, and that hides the difference you care about at this size.

Outer edge or inner edge of the levee?

This matters more than GPS. If you tap the outside of the levees you measure the whole lot; tap the inside and you measure the water and the crop. With a levee about 0.4 m wide on each side, the inner rectangle shrinks by 0.8 m each way, from 3,003 m² to about 2,899.6 m² (2.92 tan). That is 103.4 m² of ridge, 3.4 % of the paddy.

Pick one and stick to it for every paddy: the outer edge for anything to do with the land itself, the inner edge when working out seedlings or fertiliser.

Why not walk the levee

Walk Mode works on a paddy: tap the walking-figure button and walk the ridge, the line draws itself. But the GPS margin line shows why it is not trustworthy at this size. With the badge at ±4m the margin is ± 520.2 m², about 17 % of the paddy. On a smaller 10 a paddy (1,001 m²) the same ±4 m gives ± 280.1 m², 28 %.

GPS margin when walking the 3,003 m² paddy (perimeter 260.1 m × accuracy ÷ 2)
BadgeGPS marginShare
±3m± 390.1 m²13 %
±4m± 520.2 m²17.3 %
±5m± 650.2 m²21.7 %

Walking a levee also means walking a narrow, wet line, and every wobble adds length. Walk only when the satellite photo is out of date, for example after the blocks were redrawn.

Steps

  1. Settings > Units > Area: pick Square Meters (m²).
  2. Map tab, round map button, Satellite. Zoom until the paddy fills most of the screen.
  3. Measure > Measure Area. Name the project after the paddy in the New Project sheet, then Create.
  4. Tap the four corners in order around the paddy, all on the same edge of the levee. With only two taps the panel says Add at least 3 points to close an area.
  5. Drag a white handle if a corner sits a little off, then tap the green checkmark.

What it cannot do for a rice farmer

  • No tan, se, are or tsubo unit; convert by hand as in the table.
  • No parcel register data and no import of official block outlines. It measures what you tap.
  • The free version holds one measurement per project, so each paddy needs its own project, and the Projects tab allows 3 active ones. LandMeasure Pro puts every paddy in one project with a Total Area, adds file export and the PDF Report, and removes ads.
  • It cannot subtract the levees or a shed for you. Measure the inner edge instead.

A paddy this size is too small to walk well and too irregular, once the levees curve, for a tape to make much sense. Four taps on the satellite view settle the square metres, and from there you divide into tan or tsubo however your district counts.

Questions and answers

How do I measure a paddy field without a tape?
Trace it on satellite imagery: Measure > Measure Area, tap each corner of the levee in order, and read Area. On a 30 × 100 m paddy that gives 3,003 m² in four taps.
What is the size of a rice paddy in Japan?
It varies a lot. Consolidated blocks are often about 30 × 100 m (30 a, about 3 tan), while older or terraced paddies are much smaller and irregular. Measure yours rather than assume.
How do I convert tsubo to square meters?
1 tsubo is 400/121 m², about 3.3058 m². So 1 se (30 tsubo) is 99.17 m² and 1 tan (300 tsubo) is 991.7 m². LandMeasure shows m², so divide its figure by 991.7 for tan.
Which land measurement units are used in Japan?
Official figures use m², ares and hectares. Farmers still talk in tan, se and cho, and buildings in tsubo. The app shows m² and ha, not the traditional units.

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