Fence Picket Calculator

The Fence Picket Calculator helps you work out exactly how many fence pickets you need for your project and how to space them evenly along a given length. Whether you are building a new garden fence, replacing a section of panels, or planning a decorative screen, this tool saves you from the guesswork of measuring and adjusting on site.

What This Calculator Does and When to Use It

The Fence Picket Calculator takes three key measurements from you: the total length of the fence (from end post to end post), the width of each picket, and the gap you want between pickets. It then calculates the number of pickets required and the precise spacing needed to fit them evenly. You can also work backwards: if you already have a set number of pickets, the calculator will tell you what gap to leave.

Use this calculator whenever you are planning a new fence installation or replacing an old one. It is especially helpful for projects where consistent spacing matters, such as privacy fences, boundary markers, and decorative lattice-style screens. It also saves you from buying too many or too few pickets, which can delay a project or waste money.

The Formula Explained

The calculator uses a straightforward relationship between total fence length, picket width, gap size, and number of pickets. The basic formula for the total occupied length is:

Total fence length = (number of pickets × picket width) + (number of gaps × gap width)

Where:

• Number of gaps = number of pickets + 1 (because there is a gap at each end)
• Picket width is the actual width of one picket board, usually between 90 mm and 150 mm (3.5 to 6 inches) depending on the style
• Gap width is the space between two pickets, typically 25 mm to 75 mm (1 to 3 inches)

If you want to find the number of pickets when you already know the gap, you rearrange the formula:

Number of pickets = (total fence length + gap width) / (picket width + gap width)

This equation accounts for the fact that the last gap falls after the final picket. The calculator then rounds the result to give you a whole number of pickets and checks whether the spacing remains even.

For example, if your fence is 3.6 metres long (about 12 feet), your pickets are 100 mm wide (4 inches), and your desired gap is 30 mm (just over 1 inch), the calculation proceeds like this:

• Convert everything to the same unit (millimetres): 3.6 m = 3600 mm
• Picket width + gap width = 100 + 30 = 130 mm
• Number of pickets = (3600 + 30) / 130 = 3630 / 130 = 27.92
• Round to 28 pickets
• Now find the actual gap: (3600 - (28 × 100)) / (28 + 1) = (3600 - 2800) / 29 = 800 / 29 = 27.6 mm

The calculator does this automatically and shows you both the number of pickets and the final spacing.

Worked Examples

Example 1: Front Garden Fence

You are building a front garden fence that measures 4.2 metres (about 13 feet 9 inches) between end posts. You have chosen pickets that are 95 mm wide (roughly 3.75 inches) and you want a gap of 35 mm (about 1.4 inches) for a semi-private look.

Using the formula:

• Total length = 4.2 m = 4200 mm
• Picket width = 95 mm
• Gap width = 35 mm
• Number of pickets = (4200 + 35) / (95 + 35) = 4235 / 130 = 32.58
• Round to 33 pickets
• Actual gap = (4200 - (33 × 95)) / (33 + 1) = (4200 - 3135) / 34 = 1065 / 34 = 31.3 mm

You will need 33 pickets, and the final gap between each picket will be about 31 mm (1.2 inches). This is slightly tighter than your original target of 35 mm but still gives a good visual appearance.

Example 2: Privacy Screen with Fixed Number of Pickets

You have salvaged 40 pickets from an old fence, each 110 mm wide (4.3 inches), and you want to build a privacy screen for a 5-metre stretch (16 feet 5 inches). You need to know what gap to leave.

Rearrange the formula to solve for gap width:

• Total length = 5 m = 5000 mm
• Number of pickets = 40
• Picket width = 110 mm
• Total width of all pickets = 40 × 110 = 4400 mm
• Remaining space for gaps = 5000 - 4400 = 600 mm
• Number of gaps = 40 + 1 = 41
• Gap width = 600 / 41 = 14.6 mm

You will need to leave a gap of about 15 mm (just over half an inch) between each picket. This produces a very tight fence with minimal visibility through it, perfect for privacy.

Common Mistakes to Avoid

Mistake 1: Mixing units. The most frequent error is using millimetres for picket width and metres for fence length without converting. Always work in the same unit. If you measure the fence in metres, convert to millimetres (multiply by 1000) before calculating. The calculator handles this automatically, but if you are doing it by hand, stay consistent.

Mistake 2: Forgetting the extra gap. Many people assume the number of gaps equals the number of pickets. In fact, you always have one more gap than pickets because there is a gap at the start and the end. Forgetting this leads to pickets that do not reach the end posts.

Mistake 3: Rounding too early. If you round the number of pickets from 27.92 to 28, that is fine. But if you round the gap calculation at an intermediate step, the final spacing may be off by several millimetres. Always keep the full decimal until the end, then round sensibly (usually to the nearest millimetre or sixteenth of an inch).

Mistake 4: Ignoring end posts. The formula works for the space between two end posts. If your end posts are round or thick, measure from the inside face of one post to the inside face of the other. Including the post width in the total length will give you too many pickets and a crowded look at the ends.

Frequently Asked Questions

What if my pickets are not all the same width?

If you are using reclaimed or irregular pickets, measure each one individually. It is often easier to sort them into groups of similar width and calculate each section separately. For a uniform appearance, using pickets of the same width is strongly recommended.

Can I use this calculator for horizontal fences?

Yes, the same principle applies if you are installing horizontal boards between posts. Just treat the total height of the fence as the length and the board width as the picket width. The gap then becomes the space between horizontal rows.

Do I need to account for the thickness of the pickets for spacing?

No. The picket thickness (depth) does not affect the horizontal spacing along the fence line. It only matters for how much the pickets overlap or how far they sit from the posts. The calculator concerns itself only with width and gap.