Measuring trees

Height is measured in metres, either by laser clinometer or by traditional tape-and-trigonometry methods. Laser instruments are now the standard — a surveyor measures the angle to the top and base of the tree from a known distance, and the instrument calculates the height directly.

Accuracy depends on conditions. A clear sightline to the true top matters. Crowded woodland, cloud cover, and dense canopy all introduce error. Wind moves the crown of a tall tree. Height also changes over time — trees grow, and measured tops shift as new leaders emerge or old ones die back.

A height figure is always the height at the time of survey. An older measurement from a healthy tree should be read as a minimum, not a ceiling.

Girth is measured at breast height — 1.5 metres from the ground in the UK convention, 1.3 metres in some international standards. The tape is passed around the trunk at that point.

Multiple stems complicate this. A coast redwood that has coppiced into several large stems can be measured each stem separately, or all together at their shared base — two approaches giving very different totals. Different recorders handle this differently. We note the method where it is known.

Buttressing, root swells, and uneven ground all affect where the tape sits. Girths between sources are worth comparing with some caution.

A champion tree is the largest recorded specimen of a species in a given territory. In the UK, the Tree Register of the British Isles maintains champion lists for height and girth separately — a tree can hold one record without holding the other.

A tree becomes a champion by being measured and submitted. Trees can lose their status if a larger specimen is found, or if the champion itself has declined. They can also regain records as previously unmeasured trees are surveyed for the first time.

UK champion status is a useful signal, not a guarantee of absolute size. There are almost certainly unmeasured trees that would displace current record holders if surveyed.

Measurements on this map are drawn from published sources where available — the Tree Register of the British Isles, arboretum and estate records, and Forestry Commission surveys. Where multiple sources give different figures, we use the most recent credible measurement and note the source.

Where no precise figure is available but the tree is clearly substantial, we note an estimate. Estimates are derived from site records, photographs, or comparisons with nearby measured trees. We flag these clearly in the place entry.

Our aim is to give you a reliable working picture, not a definitive database. If you visit a tree and have a better measurement, we want to hear from you.