Where the gate goes when it is open
The question a slide gate answers is where the leaf lives when the entrance is open, and the answer is always the same: in a straight line behind the opening. A fourteen foot opening needs a leaf a bit longer than fourteen feet, because it has to overlap the far post rather than butt against it, and that whole leaf has to travel back past the near post. So the minimum backspace is the leaf, and the minimum frontage for the entrance is roughly twice the opening.
A cantilever gate is longer still. It carries itself on two roller posts on the backspace side and nothing touches the ground across the opening, which is why it works over a rutted or snowy driveway where a ground track would fill up and jam. The price is the counterbalance tail — the section behind the rollers that holds the rest up. Tail lengths are set by the gate manufacturer for the span and the gate weight, and a common shape is a tail somewhere around a third to a half of the opening. Take the actual number from their drawing; nothing on this page is a substitute for it.
The two roller posts do not share the load evenly
This is the part that surprises people looking at a cantilever gate for the first time. The gate is a beam on two supports with a long overhang on one side. Almost all of the weight lands on the outer roller post, the one nearest the opening, and the inner one is usually being pulled upward rather than pushed down. That is not a fault, it is how the thing works — but it means the inner post has a completely different job from the outer one, and a footing that is fine for holding weight down is not automatically fine for resisting uplift.
The calculator reports both figures as plain statics from the weight and spacing you entered. It does not say whether a post will do it. That is the gate manufacturer's specification and the installer's work, and on a heavy gate it is often an engineered detail.
Rolling gates and what the track costs
| Rolling on the ground | Cantilever | |
|---|---|---|
| Backspace | Leaf length plus clearance | Leaf plus tail plus clearance |
| Ground across the opening | Needs a clear, level track line the whole way | Nothing touches the ground |
| Snow, mud, gravel | Track fills and the gate stops | Unaffected by what is on the ground |
| Weight path | Down through the wheels into the track | Into two roller posts, one of them in uplift |
| Frontage used | Less | More |
A ground track runs the full travel — the opening plus the overlap — and it has to stay clear. In a climate with snow that is a real maintenance job every winter, and it is the reason cantilever gates dominate in the north. In a dry climate a V-track is cheaper and takes less frontage.
Frontage is the constraint people run out of first
Add it up before you commit. A fourteen foot opening with a five foot tail and a foot of clearance behind wants roughly thirty four and a half feet of straight, unobstructed fence line at the entrance, all of it on the same side. If the driveway meets the road at an angle, if there is a mailbox, a utility pedestal, a tree or a change of level in that run, the gate does not fit and no hardware choice changes it. That is the moment to price the arc instead, on the swing gate clearance calculator.
The rest of the entrance has its own arithmetic. How far the gate should sit back from the road so a vehicle waits clear of traffic is on the gate setback and stacking calculator. Posts and concrete down the fence line either side are on the fence post calculator, and the fence itself on the chain link or privacy fence pages.
What is not here
A powered gate is a machine. It moves a heavy leaf under motor power across ground where children, pets and people on foot are, and the ways it injures and kills are well documented: a person or a limb caught between a closing leaf and a post, a child riding or climbing a leaf, a hand in the path of a rolling gate at a roller post. Which safety devices an installation requires, where they go, how the operator is set up and how any of it is tested belong to the operator manufacturer's instructions and the safety standard the operator is listed to, and to the installer who does the work. None of that is on this page and this page will not summarise it. If you are considering a powered gate, that conversation starts with a gate automation installer and the manufacturer's manual, before any of the arithmetic here matters.
The strip between the travelled road and your property line usually is not yours. Whether a gate, a pillar, a post or a culvert may sit there at all, how far back from the pavement edge it has to be, what sight lines have to stay open, whether the entrance needs a permit or an encroachment approval, and who is liable for what afterwards are decided by the road authority — a city or county public works department, a state highway department, or a homeowners association on a private road — and they differ between adjacent jurisdictions. Ask them before anything is built. A gate or a column standing where a vehicle can hit it is a hazard to the driver as well as to your wallet.
Questions people ask
How much room does a sliding gate need behind the opening?
At least the length of the leaf, which is the opening plus the overlap past the far post. For a cantilever gate add the counterbalance tail on top of that, and add whatever clearance you want at the far end so the gate is not hard against something when open. In round numbers a rolling gate wants about twice the opening in total frontage, and a cantilever gate more.
How long is the counterbalance tail?
It is a manufacturer figure and it is not something a web page should invent for you. It depends on the span, the gate weight, the frame design and the roller spacing, and the gate supplier specifies it on their drawing for the gate you are buying. Common tails sit somewhere around a third to a half of the opening, which is useful for a first sanity check on whether the frontage exists, but the drawing governs.
Why is one roller post being pulled upward?
Because a cantilever gate is a beam with a long overhang. Nearly all of the weight bears on the outer roller post nearest the opening, and the inner post holds the tail end down against the leverage. The uplift figure the calculator shows is plain statics from the weight and the spacing you entered. Whether a post and its footing handle it is the manufacturer specification and the installer decision, not a conclusion from this page.
Rolling or cantilever?
Ground conditions usually decide it. A rolling gate needs a clean, level track line across the whole opening and takes less frontage, which is fine on a paved drive in a dry climate. A cantilever gate does not touch the ground at all, so snow, mud, gravel and a rutted drive stop mattering, at the cost of a longer run of fence line for the tail. In snow country cantilever wins for that one reason.
Does the clear drive-through equal the opening?
No. Guide rollers, the catch assembly and the leading edge all sit inside the posts, so the width you can actually get a vehicle through is a few inches narrower each side. The calculator takes that off separately using the figure you enter, because it varies a lot between hardware sets and it is the number that matters when you are towing something wide.