Spread betting account stakes vs lots

Hi,

I'm currently developing a bot that is linked to my Pepperstone Spread Betting account (Spread Betting is only applicable in UK) and this works on stake size not lots e,g go long EURUSD 1 stake (equivalent to £1.00per point) or 0.5 stake (equivalent to 50 pence per point).

When placing orders through the API, it's expecting the volume amount not the stake amount so I need to understand how to calculate the equivalent volume.

I'm not sure whether this should be the equvalent lot size and how to correctly calculate it. For example, would 0.5 stake be equivalent to a lot size of 5000?

When I hover over the position in the UI it looks like the trade value is denominated in GBP not the equivalent lot size.

Please can you explain what the correct formula would be and also how this would work across Indices and Commodities not just Forex.

Many thanks.