Quercus robur is a large deciduous tree, with circumference of grand oaks from 4 metres (13 feet) to an exceptional 12 m (39 ft). The Majesty Oak with a circumference of 12.2 m (40 ft) is the thickest tree in Great Britain,[5] and the Kaive Oak in Latvia with a circumference of 10.2 m (33 ft) is the thickest tree in Northern Europe.[citation needed] The largest historical oak was known as the Imperial Oak from Bosnia and Herzegovina. This specimen was recorded at 17.5 m in circumference at breast height and estimated at over 150 m³ in total volume. It collapsed in 1998.[6] The species has lobed and nearly sessile (very short-stalked) leaves 7–14 centimetres (3–5+12 inches) long. Flowering takes place in mid spring, and the fruit, called acorns, ripen by mid autumn. The acorns are 2–2.5 cm (34–1 in) long, pedunculate (having a peduncle or acorn-stalk, 3–7 cm (1–3 in) long) with one to four acorns on each peduncle.

It is a long-lived tree, with a large wide spreading crown of rugged branches. While it may naturally live to an age of a few centuries, many of the oldest trees are pollarded or coppiced, both pruning techniques that extend the tree’s potential lifespan, if not its health.[citation needed] Two individuals of notable longevity are the Stelmužė Oak in Lithuania and the Granit Oak in Bulgaria, which are believed to be more than 1500 years old, possibly making them the oldest oaks in Europe; another specimen, called the ‘Kongeegen‘ (‘Kings Oak’), estimated to be about 1,200 years old, grows in JaegersprisDenmark.[7] Yet another can be found in KvillekenSweden, that is over 1000 years old and 14 m (46 ft) around.[8] Of maiden (not pollarded) specimens, one of the oldest is the great oak of IvenackGermanyTree-ring research of this tree and other oaks nearby gives an estimated age of 700 to 800 years. Also the Bowthorpe Oak in LincolnshireEngland is estimated to be 1,000 years old, making it the oldest in the UK, although there is Knightwood Oak in the New Forest that is also said to be as old. The highest density of Q. robur with a circumference of 4 m (13 ft) and more is in Latvia.[9]