An American tourist will spend at least nine months in a Perth prison for driving on the wrong side of the road, killing his wife and a toddler in a crash.

Massachusetts-based Jerome Rubin, 61, thought he was on a dual carriageway on Albany Highway in Bedfordale when he collided head-on with an oncoming car on March 20.

The District Court of Western Australia heard on Friday that when Rubin saw the vehicle, he instinctively pulled right while the other driver pulled left, preventing any chance of stopping the devastating crash.

Rubin's wife of 28 years died at the scene while the couple's 21-year-old daughter, who they were visiting, suffered serious injuries.

A two-year-old girl in the other vehicle sustained life-threatening injuries and died in hospital two days later.

Her father, mother and grandfather also suffered serious injuries.

Rubin pleaded guilty on Friday to two counts of dangerous driving causing death, three counts of dangerous driving causing grievous bodily harm and one count of dangerous driving causing bodily harm.

One of his other daughters broke down sobbing in court when he was sentenced to 18 months in jail with a non-parole period of nine months.

The court heard Rubin was an extremely conscientious driver with no criminal or traffic record.

His visit to Australia was only the second time he had driven on the left-hand side of the road.

The first time was recently during a stopover in New Zealand on his way to Perth.

Judge Michael Bowden said there was no doubt Rubin was a man of good character who felt extremely remorseful but the incident was so devastating that jail was the only appropriate punishment.

Judge Bowden said there had been four road signs warning Rubin that the dual carriageway had changed to single and it was estimated he could have spent up to 50 seconds on the wrong side of the road.

He said the sentence should serve as a warning to all drivers to pay attention when on a country road.