I have a current transformer that I bought on EBAY as part of a small voltage+current meter.

Basically one of these: http://www.ebay.com/itm/AC-80-300V-100A-Blue-Lcd-Digital-Dual-Panel-Volt-Amp-MeterCurrent-Transformer-/251338181819#ht_1980wt_1399

It does not specify what the CT is rated at.

From another post I found a formula and would like to know if my calculations are correct.

You could also calculate it if you had the input current and output current. If the output current at 20A was 10 mA (0.01 A) you would divide 20 by 0.01 to get 2000.

So I live in New Zealand and I am using a FAN heater as a test bed at 1/2 heat. I believe the fan heater is 2000w at full power, and 1000w at 1/2 power.

Current AC Voltage : 233v AC Fan Heat set to 1000w which is 1000 / 233 = 4.2918 AMPS

Now cabling one of the AC cables though the CT it is producing 13.84 milliamps of AC current on my digital multimeter.

So from what I believe from the above formula :

4.2918 / 0.01384 = 310.10 turns.

So it is probably a 300:1 CT ?

Chris