Is there a standard rule of thumb for "hours worked in a year" at companies?
Off the top of my head I come up with ~ 1700 for my last salaried job:
365 - 104 (weekends) - 32 (vacation) - 10 (holidays) - 5 (sick) = 214 days or 1712 hours @8/d.
Also I think for "your salary" you should use your total compensation but maybe that's what you meant.
365 / 7 ≈ 52 (weeks) * 5 (work days per week) * 8 (hours per day) = 2080 hours per year
Given that very estimated number, vacation, holidays, and sick time all count as extra benefit.
One convenient aspect of this number is that if you go ahead and factor in 2 weeks of PTO/holidays/sick days, then the number of hours actually worked drops to 2000. That makes the mental math tremendously simple, albeit not 100% accurate: 100k salary / 2k ≈ 50 per hour
How do you account for the extra days, in my example it would be almost 300 hours' worth of value I get in addition to the salary?
If I understand you (and the other replies) correctly, the advice is to ignore the benefit value of PTO when estimating the hourly equivalent rate, then add it back in after the fact based on... something?
Is there a better formula than $TOTAL_COMP / $TIME_WORKED?
Folks get hung up on rule-of-thumb advice like hourly rate * 2.5 because they're thinking about their take-home pay and not the cost of employment. In many defense contracting roles, the "fully burdened rate" for contracts is 2.9-3.5x the employee's pre-tax pay. When switching to contracting you can compete by offering better services and by undercutting your (large company) competition -- and that's just where you start. Once you establish yourself as a better performer you can demand a higher price also.
50 weeks, 40 hours per week. Dividing/Multiplying by 2 in your head for quick estimates easy.
For more accuracy, do what you did.