Heats
samedi 11 août 2018, 03h00 GMT – 03h00 GMT
| Nom | Équipe | Temps | |
|---|---|---|---|
| 1 |  Rikako Ikee | Japan | 56.9″ |
| 2 |  Kelsi Dahlia | United States | + 0.46″ |
| 3 |  Emma McKeon | Australia | + 1.09″ |
| 4 |  Rebecca Smith | Canada | + 1.23″ |
| 5 | Mallory Comerford | United States | + 1.33″ |
| 6 | Katie McLaughlin | United States | + 1.44″ |
| 7 | Brianna Throssell | Australia | + 1.57″ |
| 8 |  Regan Smith | United States | + 1.69″ |
| 9 | Ai Soma | Japan | + 1.8″ |
| 10 | Laura Taylor | Australia | + 2.46″ |
| 11 | Yui Yamane | Japan | + 2.51″ |
| 12 | Suzuka Hasegawa | Japan | + 2.62″ |
| 13 | Sachi Mochida | Japan | + 2.78″ |
| 14 | Danielle Hanus | Canada | + 2.79″ |
| 15 | Mabel Zavaros | Canada | + 3.44″ |
| 16 | Kyla Leibel | Canada | + 4.64″ |
| 17 | Miranda Cristina Renner | Philippines | + 9.42″ |
| 18 | Gianna Vivien Garcia | Philippines | + 16.15″ |
| 19 | Mineri Gomez | Guam | + 18.99″ |
| Madeline Groves | Australia | DQ |