The airport said 2 August was its busiest day on record, where it helped to process more than 257,000 travellers.
The trend towards larger aircraft and airlines, fighting on price to get as many passengers on board as possible, has led to the jump in numbers – which was also helped by the summer school holidays.
The average seats per aircraft grew to 209.8, while the average share of seats filled for planes landing at Heathrow was up 0.4 per cent to 84 per cent.
Airport boss John Holland-Kaye used the traffic update to push the controversial plan to add a new runway to Heathrow, which still needs David Cameron’s sign off, after it was chosen over Gatwick by the Airports Commission.
Holland-Kaye said: “Every month that we delay is costing our economy £1bn. The Prime Minister has a mandate to give Heathrow the green light – let’s get on with it.”