On this site you can find my calculators for conversion between various mapping systems, Amateur Radio locator, and the UK national grid. These should work on any modern browser that supports Javascript, such as Safari, Chrome, Internet Explorer, Firefox, Opera, etc.

I have tried to make calculations as good as possible, using methods based on Ordnance Survey documents. This includes 7 parameter Helmert datum transormation so that error are minimised when dealing with the National Grid and GPS readings. All the code is embedded in the HTML files so you can download the page and run it locally. I am also expanding the sections showing how you can use this code in your own web pages or calculators.

• The PC Version, designed for any machine with a screen 640x480 or larger. This consists of a singe html file which can be downloaded to your machine and run without being connected to the net.
• Helmert transformation from local datums to WGS84. There are a limited number of datums covered, but it is easy enough to add your own local datums.
• Helmert transformation from WGS84 to local datums.
• A basic converter from GRS80 latitude and longitude to OSGB Eastings, Northings and National Grid Reference. This takes an input in GRS80/WGS84 degrees and decimals, e.g. 52.6543, as found in Google and other online mapping systems.

How do they work? I am often asked for information on how to calculate locators and the like. To make it easy, here are worked examples of common calculations.

• To convert from latitude and longitude to the UK National Grid, including geoid transformations, click here.
• To calculate in the reverse direction, click here.
• A working calculator to convert GB NGR to WGS84 latitude and longitude, click here.

Roger Muggleton, updated November 2017 email