How bad does a cut have to be to get tetanus shot?

Any skin opening: An untreated foot laceration that clogged thru the swamp, mud & dirt would be the prime illustration of tetanus risk. Yet, a simple shallow opening in the skin, contaminated by tetanus spores ( that are all around us but predominantly outside in dirt) could give you tetanus. You put yourself at risk every time you let your system weaken & the booster is simple & readily available.

Dirty: The cut would need to be deep, ie penetrating. Dirty wounds necessitate tetanus booster. And of course the time of last vaccine is important. If greater than 5 years since last dose of tetanus.

Booster?: Depending on the circumstances of the cut and when you had your last tetanus booster. They should be given every 10 years.