I recently picked up Spectrum programming and needed a way to encode floating point constants for use with the ROM calculator. Check it out here: https://github.com/neonz80/zxtools/tree/main/zxnumber.
The tool encodes to all 4 precisions, and can also decode both encoded constants and the internal 40 bit format.
The latest ZXDB update will be applied this evening at 1800 BST. The update takes around 30 minutes, and the site goes down whilst this happens.