You gotta test the breaking strength of the material you have.
Wrap it around the hook of a hanging scale with a timber hitch and pull down til it breaks recording the weight when it does. Do this with a 2 foot piece ,3 ft, 4 ft ,and 5 ft then average the breaking weights and thats the average tensile strength.
I used to make linen strings only and theres a wide range of tensile strengths even in the same size linen cord from the same company. Don't bonk yer head wih the scale.