You can use Grid InQuestII to transform a single coordinate or a batch of coordinates. It incorporates a wizard so you can even define your own input file format.
Grid InQuestII is available to install directly onto a PC, which means it doesn't have to be used online.
If you want to incorporate OSTN15/OSGM15 into other software and applications, see our OSTN15 and OSGM15 developer page.
The software is compatible with Microsoft Windows (XP, Vista, 7 and 10) 32 bit and 64 bit, OSX and Linux 32 bit and 64 bit.
It is licensed as per the BSD Licence.
OSTN15/OSGM15 replaced previous models OSTN02/OSGM02 in August 2016. Read about the change (PDF).You can also download the old Grid InQuest software (ZIP).