The panel decides the size, and it decides it first
Every modular enclosure is built from a fixed module, so the only sizes available are whole multiples of that module. Ask for a 20 by 10 ft run out of 6 ft panels and the arithmetic hands back 24 by 12: four panels on the long side because three would only reach 18, two on the short side because one reaches 6. That is 12 panels, 288 sq ft of floor, and 72 ft of perimeter. The four extra feet on the long side and the two on the short side are not a mistake — they are the only thing 6 ft panels can do with that request.
This runs the other way too, and usually more usefully. If the space is fixed, divide it by the panel length and take the whole number below rather than above. A 22 ft long spot takes three 6 ft panels and leaves 4 ft, not four panels; that leftover 4 ft is where a narrow gate or a filler section goes.
Round pens are polygons
Panels are straight, so a ring of them is a regular polygon and it has two diameters. Across the flats — the inscribed circle, midpoint of one panel to midpoint of the panel opposite — is the narrowest way across and the number that describes the usable space. Across the corners, joint to opposite joint, is larger. For a ring of n panels each s long, the flats measure s divided by the tangent of 180/n degrees, and the corners measure s divided by the sine of the same angle.
Sixteen 12 ft panels is the standard 60 ft round pen. Run the numbers: 12 divided by tan(11.25 degrees) is 60.33 ft across the flats, 12 divided by sin(11.25 degrees) is 61.51 ft across the corners, the perimeter is 192 ft of panel, and the enclosed polygon is 2,896 sq ft. A true 60 ft circle is 2,827 sq ft, so the polygon is about two and a half percent larger than the circle it is named after.
| Panels | Panel length | Across flats | Across corners | Difference | Area |
|---|---|---|---|---|---|
| 12 | 12 ft | 44.78 ft | 46.36 ft | 1 ft 6.9 in | 1,612 sq ft |
| 16 | 12 ft | 60.33 ft | 61.51 ft | 1 ft 2.2 in | 2,896 sq ft |
| 20 | 12 ft | 75.77 ft | 76.71 ft | 11.3 in | 4,546 sq ft |
| 24 | 12 ft | 91.15 ft | 91.94 ft | 9.4 in | 6,563 sq ft |
Notice how the gap between the two diameters closes as panels are added. At 12 panels it is over a foot and a half; at 24 it is under ten inches. The more panels in the ring, the closer the polygon gets to the circle, which is why small pens made of long panels feel distinctly angular and large ones do not.
A closed ring has one joint per panel
This trips people up when they order hardware. A straight fence of 12 panels has 11 joints. A closed ring of 12 panels has 12, because the last panel joins back to the first. At two pins or clamps a joint that is 24 pieces rather than 22, and if a post carries every joint it is 12 posts rather than 11. The difference is one, it is always one, and it is always the one you drive back to the store for.
The gate leaf sweeps a radius equal to its own width
A 3 ft leaf needs 3 ft of clear floor on the side it opens to, and swinging through a quarter turn it sweeps 7.1 sq ft. On a 288 sq ft run that is two and a half percent of the floor that cannot hold a water bucket, a feeder or a bedded corner. Two gates, or a leaf that folds back flat against the panels, doubles it. The swing also decides which way the gate can open at all: into a run that has a wall of the building on one side, a leaf that opens inward is the only option, and that is a decision made when the ring is laid out rather than when the gate arrives.
The other half of the gate question is what a narrow leaf does to the bay it sits in. A 3 ft leaf in a 6 ft bay leaves 3 ft of open panel line. Something has to fill that, and the filler is where the mesh spacing changes, where the frame is a different section, and where a limb finds a gap that the panels themselves do not have. Ordering the gate as a full-bay panel with the leaf built into it avoids the whole problem and usually costs less than the filler does.
Where this hands off
This page stops at the panels. If the enclosure is a permanent fence line rather than a panel ring, the fence post calculator and the chain link fence material calculator do posts, fabric and rails, and the gate sag brace calculator handles a wide swinging leaf that wants to droop. For the space question this page deliberately does not answer, the dog run size calculator takes your own square-feet-per-dog figure and works out an area from it, and the chicken coop size calculator does the same for a flock. Surfacing the floor is in the dog run page as well.
Questions people ask
How many panels do I need for a 60 ft round pen?
Sixteen 12 ft panels, which give 60.33 ft across the flats and 61.51 ft across the corners. Fifteen would give 56.5 ft across the flats and seventeen would give 64.2, so sixteen is the ring that clears 60 without overshooting far. If your panels are 10 ft, nineteen of them give 60.4 ft across the flats. The calculator finds the smallest ring that clears the diameter you type, because a panel ring cannot land on an arbitrary number.
Why does my run come out bigger than I asked for?
Because panels do not get shorter. Each side rounds up to the next whole panel, so a 20 by 10 ft request built from 6 ft panels becomes 24 by 12. If the space is what is fixed rather than the size you want, work the other way: divide the available length by the panel length and take the whole number below, then use the leftover for a gate bay or a filler. The calculator shows how much each side grew so you can see whether the overshoot fits.
Should I use clamps between panels or a post at every joint?
That is a question about the ground and the load, not about arithmetic, and this page counts both without preferring either. What the count shows is the scale of the difference: a 12 panel ring is 12 joints, which is 24 clamps at two apiece or 12 posts. Posts mean 12 holes, and if they are set in concrete that is a different project with a different cost. Panel makers publish what their panels are rated to be joined with and how they are meant to be anchored, and that is the answer that matters.
Does the calculator tell me if the run is big enough for my dogs?
No, and it will not. Space per animal is not arithmetic, it depends on the animal, the species, how long they are in there and what the licensing authority where you live says, and no page should hand you a number for it. Get that figure from your veterinarian, your extension service or the breed association, then use the dog run size calculator, which takes your square feet per dog and turns it into an area. This page starts after that decision and turns an area into panels.
What size gate leaf should I order?
Order it as wide as the bay if you can. A leaf the full width of a panel means no filler section, no change in mesh spacing partway along the run, and a clean joint at both ends. A narrower leaf leaves a gap in the bay that has to be filled with something, and the filler is the least tidy part of most panel enclosures. Against that, a wider leaf sweeps more floor: swing area goes with the square of the width, so a 6 ft leaf sweeps four times the floor of a 3 ft one on a quarter turn. If a wheelbarrow has to get in, the wide leaf usually wins anyway.