"There are so many stresses when you are a parent, and just trying to combat being out and about without freaking out," she said.
Mrs McMenamin, a banker, launched the program last month after six months of research.
The app has a map of New Zealand showing almost 200 locations to help parents find the best and closest baby changing areas.
She found the sites through her own travels, help from friends and information from councils.
Between 60 per cent and 70 per cent of councils replied, but she is waiting for responses from the Auckland, Hamilton and Christchurch councils.
The Wellington City Council responded with 56 locations with baby changing areas.
Rochelle Gribble, editor of parenting information website Kiwi Families, said it could be extremely hard to find good facilities. Those in women's toilets were no good for fathers, and others were in places where they were unsafe or grotty.
"Today I was out with my two girls and trying to find somewhere where my big girl needed to go to the toilet and I needed to change my little girl ... It can be really stressful to find somewhere that is contained and safe and that you can fit the buggy in."
"Sometimes when you're out you just have to change them where you change them and you deal with that. But it definitely can add to the stress, and if you've got a crying baby and you know you've got to change them it just makes the whole business much more stressful."
The nappy app
• Can find more than 150 sites with baby changing facilities
• Uses GPS to locate where the parent is in relation to the nearest changing table.
• Gives ratings of 1 to 5 for ones the founder has visited.
• Is available only for Android smart phones.
• Costs $2.50 to download.
For more information, see: Facebook.com/KiwiKidsites