Gate openers are rated based on the length or the weight of a gate. Some times it is a fixed scale, meaning the gate opener is rated for a length and a weight. For example if a gate opener says 12 feet AND 400 lbs, the manufacturer is saying that the gate can be both. Some times it is a sliding scale, meaning the gate opener is rated for a length or a weight. For example if a gate opener say 12 feet OR 400 lbs then at 400 lbs the gate should be shorter and a 12 feet the gate should be lighter. All the gate openers with this type of rating on GateCrafters.com have the sliding scale is the listing of the gate opener. In either case you never want to exceed the ratings. Even if your gate is very light the gate opener will not have sufficient leverage on the gate because of the length. So the weight of the gate, although light, has a magnified impact on the gears and motor of the opener causing additional wear and most likely will cause unexpected obstructions.