Replacement Slat Calculator

Calculator Inputs

Number of sections

Example: panels or bays along the fence line.

Section length

Section length unit

Slat width

Gap between slats

Slat dimensions unit

Slat height

Slat thickness

Waste allowance (%)

Covers cutting errors and damaged pieces.

Extra slats (optional)

Adds extra pieces beyond waste percentage.

Cost per slat (optional)

Rails per section

Common: 2 rails, taller fences may use 3.

Rail cost per meter (optional)

Estimated using total fence length × rails per section.

Fasteners per slat

Example: 2 rails × 3 screws each = 6.

Fastener pack size

Fastener pack cost (optional)

Finish coverage (m² per liter)

Use the can label; adjust for rough timber.

Finish cost per liter (optional)

Coat both sides?

Backside coating improves weathering resistance.

Example Data Table

These sample values show typical garden fence slat planning.

Sections	Section Length	Slat Width	Gap	Slat Height	Waste	Final Slats	Finish (L)
3	2.40 m	90 mm	10 mm	1200 mm	7%	79	17.06
5	1.80 m	70 mm	8 mm	1000 mm	10%	143	20.02

Formula Used

The calculator estimates how many slats cover each section length.

1) Slats per section

n = ceil((L + G) / (W + G))

L = section length, W = slat width, G = gap. This rounds up to ensure coverage.

2) Waste allowance

total = ceil((n × sections) × (1 + waste%/100)) + extra

3) Finish quantity

area = slats × (W × H) × sides liters = area / coverage

Area uses square meters; sides is 2 if both faces are coated.

How to Use This Calculator

Measure one fence section length and count how many sections you have.
Measure slat width, height, thickness, and the desired gap.
Set a waste percentage for cuts, knots, and damaged pieces.
Optional: add costs for slats, fasteners, rails, and finish.
Click calculate, then download CSV or PDF for purchasing.

Sizing slats for consistent fence rhythm

Replacement planning starts with a repeatable “pitch” made from slat width plus the gap. The calculator rounds up slats per section so coverage meets or exceeds the measured span. This prevents ending a panel with an awkward oversized gap or a forced rip-cut.

Waste allowance that matches real jobsite losses

Outdoor timber work routinely loses pieces to knots, splits, misdrilled ends, or inaccurate cuts. A modest waste factor keeps the purchase list resilient, especially when boards are pre-primed or stained. If you expect heavy trimming around posts, raise waste or add extra slats explicitly.

Fastener and rail quantities for stable attachment

Fasteners drive both durability and cost. Using fasteners per slat lets you model two-rail or three-rail builds. Rails are estimated from total fence length multiplied by rails per section, providing a quick linear-meter figure. Align fastener type with timber species and weather exposure to reduce corrosion risk.

Finish coverage for better weathering performance

Finish quantity is based on coated area from slat height and width, multiplied by one or two faces. Rough-sawn wood absorbs more product, so use label coverage as a starting point and add margin for texture. Coating both sides reduces cupping and improves long-term color consistency in gardens.

Example data for procurement and budgeting

Scenario A: 3 sections, 2.40 m each, 90 mm slats, 10 mm gap, 1200 mm height, 7% waste. Result: 79 slats and about 17.06 L of finish (two faces at 10 m²/L). Scenario B: 5 sections, 1.80 m each, 70 mm slats, 8 mm gap, 1000 mm height, 10% waste. Result: 143 slats and about 20.02 L of finish (two faces at 10 m²/L).

Tip: If your last slat lands tight to a post, increase gap slightly or reduce slat width to keep spacing uniform.

FAQs

1) Why does the calculator round up slats per section?

Rounding up ensures the slat-and-gap pattern covers the full measured section length without leaving an uncovered remainder. It also reduces the chance of ending with an oversized gap or a forced narrow slat.

2) What waste percentage should I use for garden fences?

For straightforward replacements, 5–10% is common. Increase it if you will trim around posts, work with lower-grade timber, or need color-matched boards where selection and rejects are more likely.

3) How do I choose fasteners per slat?

Count rail lines and fasteners per rail. Two rails with three screws each equals six fasteners per slat. Add more for taller slats, windy sites, or when using thinner boards.

4) Should I coat both sides of each slat?

Coating both faces improves moisture balance and reduces cupping, splitting, and uneven fading. If only the front is visible, one face can be acceptable, but durability generally improves with two-face coverage.

5) Does gap size affect how many slats I need?

Yes. Larger gaps increase the pitch (slat width plus gap), so fewer slats may be required for the same section length. Always confirm the gap is acceptable for privacy, pets, and local codes.

6) How accurate is the finish liters estimate?

It is a planning estimate based on coated area and stated coverage. Rough surfaces, end grain, and multiple coats increase usage. Use the estimate to buy product, then keep a small contingency for touch-ups.

7) Can I use this for screens, trellises, or planter surrounds?

Yes. Treat each panel as a “section” and enter its length and slat spacing. For non-vertical layouts, the quantity logic still works because it is based on repeating width-plus-gap coverage across the span.