Does anyone know of a formula to calculate transition levels from local QNH given a specific transition altitude? There are tabels that will give you a matrix showingTA's with corresponding TL's depending on various ranges of QNHThey are all rounded to units of 500 feet.TL 30, 35, 40, 45 etc. up to 100I am wondering how they make this tabel and program that in XML.Roelof

For what country? This will all depend on what country you're in and what the base TL is. E.g. here in Australia, A100. But in the US, A180. In New Zealand it's FL110 to FL130.Daz

>For what country? This will all depend on what country>you're in and what the base TL is. E.g. here in Australia,>A100. But in the US, A180. In New Zealand it's FL110 to>FL130.Thanks Daz but that is not the point. Example:I fly from Amsterdam Schiphol to London Heathrow or Australia for that matter but let's stick to Amsterdam and London.My tabel says that in the Nehterlands the TA is always 3000.Depending on the Local QNH you can then have TL's varying from 30 to 60. When descending for Heathrow I know that the London area always uses a TA of 6000. My tabel gives me, depending on the Local QNH at Heathrow a variety of TL's varying from 60 to 90 also with intervals of 500 ft. 60, 65, 70 etc.My question: Is there a formula to produce that tabel?Purpose: Program this in an XML gauge so when I give it 6000 and the Local QNH it will come up with the appropriate TL after which my altimeter will be updated with the local QNH automatically when reaching that calculated TLOf course I could put the whole table in the gauge but I am looking for a more subtle solution.Are you still with me... :-)Roelof

Found what I was looking for.Remember that 1hPa pressure difference is about 30 feet and that you need at least a 1000 feet transition layer.Example: If the transition altitude of your airport is 9000 feet, and you have a local barometric pressure of 1000 hPa, you would make the following calculation:1013 hPa