Hello RiskonFx, thanks for responding.
Wikipedia says retail is 10% of spot market = $160 billion.
USA makes up 19% of volume about = $32 billion.
Forexmagnates shows Oanda as having 22% of national accounts = $7 billion.
7 divided by 160 = 4.4%
I know this is back alley math, but is it possible Oanda is 4.4% of retail volume?
They may have 22% of accounts, but if they don't pass orders into the Spot Market then this means very little. Most retail brokers don't pass client orders outside of the broker and settle in house, netting off longs against shorts. It's quite a complex area and certainly isn't what it seems at face value. Retail broker data is almost always skewed, grey and not representative of the entire picture.
As Xela mentioned, you can find quantified volume in fx futures. She knows far more than I do in that area.