I walked the talk by cutting the SIM to Micro-SIM myself with this measurements and tested it to be working.
*I take no responsibility for any damage to your SIM card, mobile phone, iPad or any other equipment.
IMPORTANT: Print 1-to-1 on an A4 size paper and follow the instructions.
Print out this free template
Remember to round the corners opposite the notch carefully or I recommend to use a nail filer or sand paper. Good luck!
Here is a link to Micro-SIM cutters in Amazon if you are skeptical.
*Update: Didn't know my template link was no longer working anymore. Updated link with a working template. Apologies. Also put in a link for the Micro-SIM cutter from Amazon if you are interested. I ought to be more responsible when my image appears first in the search. Put in a video by howto.cnet for clarity.
**Update: Goodness, the German website for the template link sold off their web URL. Added 2 more links I found.