Lengnau has an area of 7.41 km² (2.86 sq mi).
 Of this area, 2.9 km² (1.1 sq mi) or 39.3% is used for agricultural purposes, while 2.66 km² (1.03 sq mi) or 36.0% is forested.
  Of the rest of the land, 1.6 km² (0.62 sq mi) or 21.7% is settled (buildings or roads), 0.12 km² (30 acres) or 1.6% is either rivers or lakes and 0.04 km² (9.9 acres) or 0.5% is unproductive land.

Of the built up area, industrial buildings made up 2.6% of the total area while housing and buildings made up 11.1% and transportation infrastructure made up 5.6%.
 Power and water infrastructure as well as other special developed areas made up 1.2% of the area while parks, green belts and sports fields made up 1.2%.
 Out of the forested land, 34.6% of the total land area is heavily forested and 1.5% is covered with orchards or small clusters of trees.
 Of the agricultural land, 32.0% is used for growing crops and  5.7% is pastures, while 1.4% is used for orchards or vine crops.
 All the water in the municipality is flowing water.

The municipality is located at the foot of the Jura Mountains in the Aare river plains.
 The old Aare river course forms the municipal border.

On 31 December 2009 Amtsbezirk Büren, the municipality's former district, was dissolved.
 On the following day, 1 January 2010, it joined the newly created Verwaltungskreis Biel/Bienne.
Lengnau has an area of 7.41 km² (2.86 sq mi).  Of this area, 2.9 km² (1.1 sq mi) or 39.3% is used for agricultural purposes, while 2.66 km² (1.03 sq mi) or 36.0% is forested.   Of the rest of the land, 1.6 km² (0.62 sq mi) or 21.7% is settled (buildings or roads), 0.12 km² (30 acres) or 1.6% is either rivers or lakes and 0.04 km² (9.9 acres) or 0.5% is unproductive land.
Of the built up area, industrial buildings made up 2.6% of the total area while housing and buildings made up 11.1% and transportation infrastructure made up 5.6%.  Power and water infrastructure as well as other special developed areas made up 1.2% of the area while parks, green belts and sports fields made up 1.2%.  Out of the forested land, 34.6% of the total land area is heavily forested and 1.5% is covered with orchards or small clusters of trees.  Of the agricultural land, 32.0% is used for growing crops and  5.7% is pastures, while 1.4% is used for orchards or vine crops.  All the water in the municipality is flowing water.
The municipality is located at the foot of the Jura Mountains in the Aare river plains.  The old Aare river course forms the municipal border.
On 31 December 2009 Amtsbezirk Büren, the municipality's former district, was dissolved.  On the following day, 1 January 2010, it joined the newly created Verwaltungskreis Biel/Bienne.
Lengnau, Bern