Building a fence looks simple from the curb — a row of pickets nailed to a couple of rails — but the maths catches a lot of people out. Get the picket spacing slightly off and you end up with a stupid 12mm offcut at the last post, or a fence that bows because the gaps were tight in summer and dried out wide by autumn. The Chippy Tools fence picket calculator does the arithmetic for you in metric or imperial, so the pickets divide evenly, the gaps stay consistent, and the fence reads as one continuous run from corner to corner.
What the fence picket calculator does
The fence picket calculator is the Equal Spacing Calculator configured for fences. Enter your total fence run, your picket width, and a target gap — the app returns the exact picket count, the precise gap that fits the run evenly, and the position of every picket along the rail. It also works in reverse: pick the picket count first and the calculator solves for the gap. There is no internet required and no rounding error — the same calculator that builders use on-site for deck balustrades and equal-spacing layouts powers this fence-specific workflow.
How to calculate fence pickets
To work out how many pickets you need, three numbers go in: the total length of the fence run, the width of one picket, and the gap you want between pickets. The formula is straightforward — picket count = run length ÷ (picket width + gap), rounded to the nearest whole number. Because pickets are sold in fixed widths (90mm and 140mm in Australia, nominal 1×4 or 1×6 in the US), the gap is the only variable that can flex to make the fence divide evenly. Chippy Tools solves for that gap automatically when you enter the run and picket width.
For a worked example, take a 6.0 metre run with 90mm pickets and a target gap of 20mm. Each “module” of one picket plus one gap measures 110mm, and 6000 ÷ 110 gives 54.5 modules. Round down to 54 pickets, then back-solve the gap: 6000 - (54 × 90) = 1140mm of gap shared across 54 spaces = 21.1mm per gap. The fence now divides cleanly across the full run without an awkward offcut at the last post.
How to calculate fence post spacing
Fence posts are usually spaced between 2.4m and 2.7m (8’–9’) apart for a 1.8m (6’) high fence. The trick is to make the post-to-post bays divide evenly across the total fence length so you don’t end up with one short bay at the end. Enter the total length and your preferred maximum post spacing into the Chippy Tools Equal Spacing calculator and it returns the actual bay length that fits — usually a few centimetres tighter than your maximum, but every bay identical. Run the picket calculation per bay so each panel is independent and any future repair only affects one section.
For longer runs the calculator handles posts and pickets together: solve for the bays first, then for each bay solve for the picket count and gap. The fence ends up uniform end-to-end with no compromise at corners or stop-ends.
Run the Numbers Before You Buy Pickets
Download Chippy Tools and use the Equal Spacing calculator to count pickets, posts, and rails for any fence run — offline, on-site, in metric or imperial.
Picket fence vs privacy fence
A traditional picket fence has wider gaps than picket width — the openness is the whole point. Typical settings are 90mm pickets with 50–75mm gaps, giving a roughly 50/50 picket-to-gap ratio. A privacy or semi-privacy fence tightens the gap to 10–20mm so neighbours and dogs can’t see through. The picket count on a privacy fence is roughly twice that of a traditional picket fence for the same run length, so material cost and build time are the main reasons to pick one over the other rather than aesthetics alone.
The Chippy Tools fence picket calculator handles both. Enter a 50mm gap for a classic picket look and a 15mm gap for a privacy fence — the calculator returns the picket count, the exact gap after rounding, and the total linear metres of picket required including a waste percentage if you want one.
Horizontal fence calculator
Horizontal slat fences flip the geometry. Instead of dividing the fence length, you divide the fence height. Most horizontal fences are built panel-by-panel between two posts, and each panel is typically 1.8m (6’) tall. With 90mm slats and a 15mm gap, the panel takes 1800 ÷ (90 + 15) = 17 slats with 12mm gaps after rounding. Wider 140mm boards drop the slat count to 11 per panel and look more contemporary; narrower 65mm boards push it past 22 slats per panel for a finer texture.
To use the Chippy Tools Equal Spacing calculator for a horizontal fence, just enter the panel height as your “total length” and the slat depth as your “picket width.” The same maths applies — the calculator solves for the gap that makes the slats fit evenly across the panel height with no thin offcut at the top or bottom rail.
Picket spacing rules and codes
Boundary fences are not safety-critical the way deck balustrades are, so most jurisdictions don’t specify a maximum picket gap. What they do regulate is fence height — typically 1.8m (6’) for side and rear boundary fences, 1.2m (4’) for front boundary fences in Australia, and similar in the US and UK. If your fence is dual-purpose (boundary fence on one side, pool barrier on the other), pool fencing standards apply and gaps are tightly controlled — see the Baluster Spacing Calculator for the relevant 100mm and 125mm sphere rules.
Some HOA covenants and council planning controls specify a minimum picket-to-gap ratio for streetscape character — 50/50 in heritage zones, 70/30 in suburban areas. Confirm before you buy materials. Chippy Tools doesn’t enforce these rules, but it does let you test different ratios in seconds so you can compare a compliant layout against your preferred look before committing.
Spacing Maths That Just Work
Chippy Tools handles fence pickets, deck balusters, equal spacing, decking layout, and more. Download once, calculate anywhere — no internet required.
Materials and waste
A typical 6.0m fence run with 90mm pickets and 20mm gaps takes 54 pickets per run. Multiply by your fence length and add 5–10% for offcuts, splits, and warped boards that you reject on-site. For posts, count one post per bay plus one for each end — a 30m fence at 3m bay spacing needs 11 posts, not 10. The picket calculator returns picket count and total linear metres; multiply by your supplier’s price-per-metre to budget the run.
Treated pine, hardwood, and composite all behave slightly differently. Treated pine pickets shrink as they dry — if you nail them tight to a 5mm gap in summer, you can end up with 12mm gaps by autumn. Build with the gap you want at year-end, not on install day. Composite and Colorbond pickets are dimensionally stable and can be set to the exact target gap from day one.
Why use a fence picket calculator on your phone
The Chippy Tools app is built for tradespeople who need calculations on-site without internet. The same Equal Spacing engine that powers the fence picket calculator also drives the Decking Calculator and Baluster Spacing Calculator, so once you’ve worked out the picket layout you can size the deck or balustrade in the same app without re-entering measurements.
Web calculators break when you’re behind a colorbond fence at the back of a property with one bar of signal — the Chippy Tools calculator runs locally on your phone or tablet and the answer is on screen in under a second. Switch between metric and imperial without restarting, save common picket and gap presets for the suppliers you use most, and pull up the calculator straight from your home screen widget when a customer asks for a quick price during the quote.
Related calculators
- Equal Spacing Calculator — the underlying tool for any evenly-divided run, including pickets, posts, shelves, and battens
- Baluster Spacing Calculator — for deck balustrades, stair railings, and pool fences where the 100mm/125mm sphere rule applies
- Decking Calculator — for sizing deck boards, joists, and bearers when the fence ties into a deck
- Equal Spacing Calculator is also useful for fence rail layouts, wire-strand spacing, and stringer post divisions