68 to 71 centimetres (27 to 28 in)Litter size. This is due to their prey-drive, their speed, and the assertion that Greyhounds have no road sense. In some jurisdictions, it is illegal for Greyhounds to be allowed off-leash even in off-leash dog parks. Due to their size and strength, adoption groups recommend that fences be between 4 and 6 feet tall, to prevent Greyhounds from jumping over them. As per most breeds being rehomed greyhounds that are adopted after racing tend to need time to adjust to their new lives with a human family. Many guides and books have been published to aid Greyhound owners in helping their pet get comfortable in their new home.