Hay bales which survived a massive bushfire north of Adelaide last week have been used by a local man to propose to his girlfriend.

Under the guise of checking bushfire damage to the family farm from the air, Ben Kemp of Roseworthy took girlfriend Jadine Mold up in a helicopter.

He told 891 ABC Adelaide it took a couple of hours to lay out his marriage proposal in a paddock beforehand.

"We were lucky enough to be spared some bales of hay, even though it was where our major hay storage was that we lost," he said.

"I set out some round bales of hay in a paddock and organised a helicopter flight for my girlfriend."

Mr Kemp said 95 per cent of the farm was fire-damaged but his plan to propose had been in his mind since before the blaze.

"Dad was the only one who knew exactly what I was doing," he said.

"I'm not normally very artistic, I drive a tractor every day but I had a picture in my head of what I wanted it to look like and it turned out better than I thought it would."

The charter helicopter pilot helped Mr Kemp keep the surprise from his girlfriend until they reached the paddock.

"Bridget the pilot said 'Well, what's going to be your excuse if she asks anything?' and I said 'Just tell her we're going to do a flyover of the farm to see the extent of the fire damage'," he said.

"I wasn't game enough to take the ring in the helicopter so I left all that in a safe spot on the ground.

"We landed and I had the ring and everything set out there and I got down on one knee."

It worked — the next step will be setting a wedding date.