The widest machine and the tallest machine are usually different machines
Take a four-machine list off a working farm: a tractor with a loader at 96 inches wide and 132 inches to the top of the cab, a round baler at 108 wide and 114 tall, a grain wagon at 102 by 126, and a pickup at 80 by 78. Add six inches of clearance each side and six overhead and the widest opening asked for is 120 inches — the baler — while the tallest is 138 inches — the tractor.
Size the door on the baler and the tractor does not fit. Size it on the tractor and you have bought two feet of width nothing uses. This is the failure that puts a permanent dent in a door track, and it happens because people size an opening off the machine they think of as the big one rather than off the list.
| Machine | Width | Opening needed | Height | Head needed |
|---|---|---|---|---|
| Tractor with loader | 8 ft | 9 ft | 11 ft | 11 ft 6 in |
| Round baler | 9 ft | 10 ft | 9 ft 6 in | 10 ft |
| Grain wagon | 8 ft 6 in | 9 ft 6 in | 10 ft 6 in | 11 ft |
| Pickup | 6 ft 8 in | 7 ft 8 in | 6 ft 6 in | 7 ft |
With six inches of clearance each side the baler asks for ten feet of width and the tractor for nine, while on height the order reverses: the tractor wants eleven and a half feet of head and the baler ten. Neither machine is the big one. A 16 by 14 door swallows all four with six feet of width and two and a half feet of head to spare — which sounds generous until the day something arrives with a folded implement on the back.
Measure the widest fixed point, not the machine
A spec sheet width is a chassis width. What actually hits the jamb is a mirror, a fender extension, a dual, a loader bucket at rest, a folded marker arm, or a bale on the forks. Height is worse: a cab roof is not the tallest thing on a tractor once a beacon, an exhaust stack or an air-conditioning shroud is on it, and a raised loader is taller again by several feet.
The number to put in this calculator is the one you get from standing in front of the machine with a tape and finding the point that sticks out furthest, in the configuration it will be in when it comes through the door. If the loader goes in raised, measure it raised. If the mirrors fold, decide now whether they will actually get folded every time, because they will not.
Depth is set by the longest machine, and it is set twice
The grain wagon at 240 inches is 20 feet long. Park two of those nose to tail with three feet between and the bay wants 43 feet of depth. A 40 ft building is three feet short, which in practice means the back machine comes out before the front one can move, every time, for the life of the building.
The same length shows up again outside. To line a 20 ft machine up square with the door you need room to straighten before you commit, and this calculator adds whatever run-up figure you enter to the machine length. Ten feet gives 30 feet of clear ground in front of the door. That figure comes from whoever drives it, not from here — the page has no model of how a machine turns. For a truck and trailer the number that actually governs is offtracking, and the trailer offtracking and turnaround calculator works that out properly. For a vehicle swinging in off a street, the driveway apron and turning radius calculator does the same job.
What this is not
It is rectangles through a rectangle, and that is all. It says nothing about whether a gap is safe to drive through, nothing about the arc a machine sweeps entering at an angle, nothing about the floor, and nothing about what happens when someone is standing between a reversing machine and a wall. Naming that as a hazard is as far as this page goes.
Once the opening size is settled, the framing it costs the wall is a separate calculation — see the door opening framing take-off — and the door hardware itself is handled by the pocket and barn door calculator for a slider or the garage door opening and headroom calculator for a sectional door, where headroom, backroom and sideroom matter as much as the opening. For fitting benches and machines inside a shop that already exists, the workshop layout planner works from in-line workpiece run instead.
Questions people ask
How much clearance should I put each side?
That is your figure and the calculator will not suggest one, because it depends entirely on who is driving, how often, how much light there is, and whether the machine is being reversed. What the page does is make the consequence visible: raising the side clearance from six inches to a foot on a 108 inch baler moves the opening asked for from 10 ft to 11 ft, and a foot of door width on a post-frame wall is not free — it can push the opening across another post line. Try two or three figures and see where the door size jumps.
Why does the calculator ask for inches when everything else is in feet?
Because machines get measured in inches and buildings get designed in feet, and converting in your head between the two is where the mistakes happen. Enter the tape reading. The output converts to feet and inches for you, so a 132 inch tractor comes back as 11 ft and a 138 inch head requirement as 11 ft 6 in, which is the form the door schedule wants. The building dimensions — door width and height, bay depth, ground out front — stay in feet because that is how they are drawn.
Does this account for a machine turning as it comes in?
No, and it should not be read as if it does. The run-up field is a straight allowance you enter yourself, added to the machine length, giving the clear ground you want in front of the door. It is not a turning circle, an offtracking calculation or a swept path. A machine that has to swing ninety degrees into a door needs far more room than its own length plus a few feet, and how much more depends on the wheelbase, the articulation and what is behind it. For a towed rig, use a proper offtracking calculation.
What if a machine has no length figure?
Leave the fourth number off and the line still counts for the door width and height, which are the two things most people are actually sizing. The depth and run-up sections use the longest machine that does have a length, so a list where nothing has a length will show zero depth needed, which is a signal rather than an answer. Lines missing a width or a height are skipped entirely and the output tells you how many, because a machine with no width contributes nothing to a door-sizing question.
Can I use this for a lean-to or an open-front bay instead of a door?
The width, height and depth arithmetic works the same way — an open bay between two posts is still a clear opening with a head height above it. What changes is that the clear width of a post-frame bay is the bay spacing minus the post section, not the bay spacing, and this page does not know your post size. Work out the clear dimension by hand and enter that as the door width. The bay spacing itself comes from the post-frame bay layout calculator on this site.