I suggest talking to other people consulting at your level. Some industry associations perform salary surveys (including for consultants) that can be used as a guide.
Going by a prior salary may result in underpayment. For myself, I found that when I became a consultant I was able to increase my income by 300%. The increase in income was due to several factors: 1) I discovered I was underpaid in my prior role 2) I was also "underemployed" so I was able to work at a much higher level than I had been when employed so my consulting roles were also worth more 3) I hustle and as a consultant I was paid for all the "overtime" I put in.
So take a broader more comprehensive look at your skills and type of work required before setting a fee.