Start with the installed opening, not the product name
An “8-foot fence panel” does not necessarily need Posts eight feet apart. The label may describe the panel itself or the distance between Post centers. Brackets and rail insertion can change the relationship again. Before ordering panels or marking Posts, find the dimensioned installation drawing for the exact series, size and Post type you intend to use.
This guide counts manufactured panels along one straight Run. A panel is the purchased assembly; a Bay is the clear opening between Posts. Keeping those terms separate matters when one panel is shortened to fill the last Bay. If you are building with individual pickets, use the picket fence planner instead. Panel arithmetic does not choose structural spans, Post sizes, foundation depths or a permitted installation method.
Keep five measurements on your worksheet
- Nominal width: the product label, such as 6 ft or 8 ft. Use it to identify the product, not as an installation measurement.
- Physical panel width: the actual end-to-end dimension of the assembly or rails, as defined in its drawing.
- Bay Clear Length: the distance between the two inside Post faces. A rail inserted into routed Posts can be physically longer than this visible opening.
- Post center-to-center distance: for equal-width Posts on a straight Run, Clear Length plus one Post width. Each center contributes half a Post width.
- Overall Length: the distance from the outside face of the first Post to the outside face of the last Post. Include both terminal Posts when reconciling the Run.
Do not add a generic bracket allowance to every panel. Some brackets occupy the existing opening; other systems need clearance or rail insertion. Write the manufacturer’s installed opening beside the actual panel dimension, even when the two happen to match. This is also why a dimension taken between existing Posts cannot simply be entered as Overall Length.
Product examples: the same label can mean different dimensions
These are examples from the named systems, not interchangeable specifications. Dimensions are inches. Confirm the current instructions supplied with your order before using them.
| System and nominal size | Physical rail width | Clear opening | Post centers |
|---|---|---|---|
| Stronghold Iron, 8 ft, 2 in Posts | 96 | 96 | 98 |
| Infinity Aluminum Traditional, 6 ft, 2 in Posts | 72.5 | 71 | 73 |
| Infinity Aluminum Signature, 6 ft, 2.5 in Posts | 73 | 71.5 | 74 |
| Infinity Aluminum Signature, 8 ft, 2.5 in Posts | 95 | 93.5 | 96 |
The Stronghold Iron installation manual, page 6 describes a 96-inch panel and a 96-inch opening: its brackets do not add another allowance to that opening. With two-inch Posts, the centers are 98 inches apart. The manual is labeled February 2015; treat its dimensions as specific to that system and verify your supplied version.
The Infinity Aluminum installation manual, page 6 distinguishes physical, visible and center-to-center dimensions. For example, its nominal eight-foot Signature panel has 95-inch rails but uses 96-inch Post centers. The rails extend into the Posts, so subtracting the rail width from the center distance would not give the Post width. These drawings explain why a universal “divide by eight” rule can produce the wrong layout.
Worked example: a 40-foot Run with a shortened last panel
Assume a level, straight Run with no Gate or Corner. Its Overall Length is 40 ft, or 480 in, measured outside face to outside face. Use two-inch Posts and a system requiring a 96-inch clear opening for each full panel. For this arithmetic example, assume the selected product can be shortened to fill the final opening; that must still be checked before purchase.
Four full panels and five Posts occupy 4 × 96 + 5 × 2 = 394 in. That is too short. Five full panels and six Posts would occupy 5 × 96 + 6 × 2 = 492 in, which is 12 inches too long. Five panel positions therefore fit the boundary only if one or more panels can be shortened.
Keeping the first four openings at 96 inches leaves:
480 − (6 × 2) − (4 × 96) = 84 in
The final Bay has an 84-inch Clear Length. Check the complete chain: 4 × 96 + 84 + 6 × 2 = 480 in. The purchase base is five full panels, with one allocated to that shorter Bay, plus six Posts of the appropriate types. Spare material is a separate decision; the example does not include damage, rejected parts or Gate hardware.
| Post | Center from first outside face (in) | Next Bay Clear Length (in) |
|---|---|---|
| 1 | 1 | 96 |
| 2 | 99 | 96 |
| 3 | 197 | 96 |
| 4 | 295 | 96 |
| 5 | 393 | 84 |
| 6 | 479 | End of Run |
The first four center intervals are 98 inches; the last is 86 inches. The final center plus half the Post width is 479 + 1 = 480 in, matching the boundary. Record all centers from the same origin instead of repeatedly stepping a rounded measurement along the Run.
An 84-inch opening is not yet a cutting instruction
Do not interpret the example as permission to remove 12 inches from one end of any panel. The Stronghold manual’s cutting instructions on page 15 require at least 1.5 inches of rail beyond the final picket for the bracket. A proposed cut can meet a picket, and some layouts require trimming both ends. The panel style and picket positions determine whether the intended shortened assembly is possible.
Check the end detail, minimum retained material, cut treatment and connection method for your exact product. If the proposed last Bay cannot be filled as planned, revise the distribution before fixing Posts. Two shorter Bays may produce a different cutting arrangement, but that alternative still needs product-specific confirmation. An offcut is not automatically another usable panel: it may lack the necessary end detail or length after cutting.
Count Gates, Corners and separate Runs explicitly
A Gate opening is not a purchased fence panel. Obtain the required opening from the leaf and hardware instructions, identify its boundary Posts, and calculate the adjacent Runs separately. Do not subtract a nominal Gate width from a site perimeter and assume the remainder divides into full panels. The Gate layout guide explains how shared Posts affect the count.
At a Corner, use the specified corner Post or connection arrangement and record that physical Post once. End, line, corner and Gate Posts may be different products even when their overall count looks correct. Sloping ground also changes the task: horizontal plan distance, distance along the slope and a stepped or racked panel installation are not the same measurement. This level-ground example does not solve those configurations.
Use the right calculator, then check the actual assembly
The Fence Post spacing calculator equalizes clear Bays after deducting Posts. It does not preserve full manufactured-panel widths or optimize panel cuts. For the example’s five Bays, equalizing would make each opening 93.6 inches, rather than four at 96 inches and one at 84 inches. That is a different cutting plan, not a more accurate version of the same one. See six-foot versus eight-foot Post spacing for the equal-Bay model.
Before ordering, complete a worksheet with the product series, Post types, Overall Length for each Run, required clear openings, full and shortened panel counts, and separately listed spares and hardware. Trial-fit a panel with its Posts and connections as directed by the manufacturer; compare the real assembly with the drawing. Resolve any dimension mismatch before committing to the remaining Post positions. Keep the worksheet with your order so a substituted panel or Post size triggers a fresh check rather than an unnoticed change.