We would advise weighing your items to the best of your ability, in order to avoid any overweight charges.
To weigh your items, we recommend weighing your box/suitcase using weighing equipment. We recommend bathroom scales or also hand-held luggage scales. They can usually be purchased via online retailers or at your local hardware goods store.
If your bathroom scales perhaps may be older and will not weigh a suitcase, you can weigh yourself holding the item you are going to send. If you then weigh yourself as normal (without the item) the difference will be the weight of your item.
If you are unsure of the exact weight, please overestimate it slightly. This is to allow some room for error.