Jodie Chesney died from an 18cm-deep wound from a knife which almost passed right through her body, a court heard.
The 17-year-old was socialising with friends in the Harold Hill area of Romford, east London, when she was stabbed in the back on 1 March.
Despite the efforts of medics, Jodie was pronounced dead in a petrol station while on the way to hospital.
Manuel Petrovic and Svenson Ong-a-Kwie, both from Romford, and two teenage boys all deny murder at the Old Bailey.
Jurors have previously heard Jodie was unlikely to have been the intended target of what is thought to have been a drug dispute.
Pathologist Dr Ashley Fegan-Earl carried out a post-mortem examination on Jodie’s body on 3 March and found she had a stab wound to the right side of her back from a “single-edged knife”.
Dr Fegan-Earl said the blade came within a few millimetres of fully penetrating through the body.
While the wound was 18cm deep, the pathologist said it was “entirely plausible a shorter blade gave rise to the longer wound track”.
He suggested “moderate force” would have been required, but added: “It does not mean severe force was not used.”
Dr Fegan-Earl recorded Jodie’s cause of death as “shock and haemorrhage due to stab wound to back of the chest”.
The pathologist was asked whether a 19.5cm black-handled, single-edge knife seized from Mr Ong-a-Kwie’s room could have caused the wound.
He said the knife was “consistent” with the fatal injury.
However, Charles Sherrard QC, defending 19-year-old Mr Ong-a-Kwie, said it was a hypothetical question as the wound could have been caused using a “bog standard kitchen knife”.
The pathologist agreed.
Dr Fegan-Earl also told jurors the injury could have been caused in a fraction of a second.
The trial continues.