# What do we really mean by put-call ratio and how should it be expressed?

I need to calculate the put-call ratio for an American option. But I'm a complete naïf: I don't know how. I think I'd use the put open interest and the call open interest. I can imagine two ways to calculate PCR:

1. Simply (as some references tell me) take OIputs divided by OIcalls and there's my number, right there:

PCR = OIputs / OIcalls

2. Or (as other sources seem to suggest) take OIputs divided by the sum of OIputs and OIcalls:

PCR = OIputs / ( OIputs + OIcalls )

Further, I don't even know if the ratio can most usefully be expressed as a decimal (i.e., 0.667) or as a fraction (i.e., 2/3) or as the ratio notation I learned in grammar school (i.e., 2:3).

What's the usual, expected, and/or "right" way to calculate PCR?

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