In November 2019, "Watermelon Sugar" debuted at number thirty-five on the
UK Singles Chart, giving Styles his third UK top 40 single at the time. In January 2020, it reached number seventeen on the chart before departing it the following month. After its official single release in May 2020, "Watermelon Sugar" re-entered the chart at number thirty-five; later ascending to a new peak of four in August 2020, becoming the second highest-charting single from the album. As of October 2020, it has 936,260 sales and has been certified platinum by the
British Phonographic Industry (BPI). In Ireland, "Watermelon Sugar" debuted at number twenty-four on the
Irish Singles Chart in November 2019, before reaching number four on the chart in June 2020. In Scotland, the single re-entered the chart at number seventy-eight in May 2020 and later peaked at number two the following month. In Greece, it debuted at 36 on 15 February 2020, however on 29 June, it peaked at number 6. After the release of
Fine Line, "Watermelon Sugar" debuted at number thirty-eight on the
ARIA singles chart in Australia; later reaching a new peak of twelve in its fifth week. After being released as an official single in May 2020, the track re-entered the chart; reaching a new peak of number six in June 2020, Harry's highest-charting single from the album. In New Zealand, the song debuted at number thirty-three and has so far peaked at number four. It has been certified platinum in both countries. In the United States, "Watermelon Sugar" debuted at number sixty on the
Billboard Hot 100 chart dated 30 November 2019. It peaked at number fifty-four after the release of
Fine Line and officially left the chart the following month. After being released as a single, "Watermelon Sugar" re-entered the chart in May at number sixty-four and reached number one on the chart dated 15 August 2020; giving Styles his first number-one single, his third top-ten single, as well as his fourth top-twenty single in the US, and third from
Fine Line. He also became the second member of
One Direction to reach number one on the
Billboard Hot 100 after
Zayn Malik with his 2016 hit "
Pillowtalk". In doing so, Styles became first British artist to top on the Hot 100 with a single that did not top the UK Singles Chart after
Adele's single "
Set Fire to the Rain" in 2012 and the first British male to match the record since
Jay Sean with his single "
Down" in 2009. The single also topped the
Mainstream Top 40 chart on the issue dated 8 August 2020, becoming the singer's second single after "
Adore You" to top the chart, remaining at the summit for seven consecutive weeks. On 7 August 2020, it was certified double platinum by the
Recording Industry Association of America. On the
Canadian Hot 100, "Watermelon Sugar" debuted at number forty-six and later reached number three on the chart, becoming his second top-ten hit from the album in Canada. ==Music video==