I am making a cake and the recipe calls for a 900g/2lb loaf tin. How do I work out if the loaf tin I have is the correct size - or how do I work out how big my tin is so I know whether to scale the recipe appropriately?
You are looking at a 8.5" x 4.5" x 2.5" (or 7.25" x 4.5" x 3.5", high sided model) bread pan. If you are looking at using a different shape, it might affect the texture of the cake, but you'll have to calculate the volume difference from there. Something around 100-114 cubic inches. (Length x width x height).
Usually the answer is to use a conversion chart. Google provides many, but this one is specific to cake pans.
In your case, though, the weight measurement is pretty non-standard. Pan conversion charts usually do things by volume. Assuming, though, a fluid ounces conversion where 8 fl. oz. is one cup, you want a 32 ounce pan, or 4 cup pan. The conversion chart will show you a variety of 4 cup pans, and also how many cups your cake tin holds, then convert that to fl. oz. and scale.