How badly do i have to bleed from a wound to need another tetanus shot?

Tetanus EVERY 5-10yr: If a wound is dirty (contaminated with dirt/wood/metal etc.) and your last tetanus shot was >5 years ago then you may need a tetanus shot. With whooping cough epidemics all over the country it is best to get a tdap shot (tetanus+whooping cough) anyway. Generally, you need a tetanus shot every 10 years no matter the situation.

Tetanus shot: Is given for injury caused by puncture wound with considerable exposure to dirt or rust, not to bleeding.You will need tetanus shot if it has been more than five years since your last one.

Not the issue: How/volume of blood is not the issue. Were you working in the soil ? Is the wound contaminated by wood/soil/other debris ? Gardeners or those working in landscape are encouraged to get boosters every 5 yrs. If you have a soiled wound and or have not kept up with your tetanus boosters you may need hyper immune tetanus globulin plus a booster.