Methodology

Planning estimates, not guarantees

Every result on FigureWright is a planning estimate built from general formulas and the values you enter. The calculators don’t know your site, soil, slope, wind exposure or local rules. Use the numbers to plan, budget and compare, then check them against your own plan, your supplier and your local requirements before you buy or build.

General principles

• One set of units inside. Inputs are converted to metres (and cubic metres) using exact factors (1 ft = 0.3048 m, 1 in = 2.54 cm), and every formula runs in those units. The same fence entered in feet or metres gives the same counts.
• No early rounding. Intermediate values keep full precision. Only final purchase quantities are rounded, and always up, because you can’t buy part of a post or a bag.
• Floating-point safety. Before rounding up, a vanishingly small tolerance is applied so that a value like 12.000000000000002 (a side effect of unit conversion) counts as 12, not 13.
• Invalid input stops the calculation. Zero or negative lengths, gates wider than the fence, holes narrower than the post and similar problems produce a message, not a number.

Fences: posts and sections

A section is the span between two posts. Corners and gates split a fence into separate straight runs.

fenced length = total length − (gates × gate width)
minimum sections = ⌈ fenced length ÷ maximum spacing ⌉
recommended sections = minimum sections + (runs − 1)
posts (open run) = sections + gates + 1
posts (closed loop) = sections + gates

A run with n sections needs n + 1 posts. Runs that meet at a corner share the corner post. The runs either side of a gate don’t share a post, because the gate opening sits between them. A closed loop ends at its starting post.

Because only the total length is known, the calculators can’t tell how each run divides. Rounding each run up separately adds at most one partial section per extra run, so the recommended figure is a safe upper bound; the minimum is shown alongside it. Actual spacing is the fenced length divided by the number of sections.

Rails

Unless you choose a number, vertical-board fences use a common rule of thumb: 2 rails per section up to 1.25 m (about 4 ft) high, 3 rails up to 2.0 m (about 6½ ft), and 4 rails above that. This is a convention, not a structural calculation. Horizontal board fences and pre-built panels are counted without separate rails.

Pickets and boards

boards = ⌈ (length + gap) ÷ (board width + gap) ⌉

A row of n boards has n − 1 gaps, so one gap is added to the length. For board-on-board, the front layer uses a gap of board width − 2 × overlap and the back layer has one fewer board than the front. For shadowbox, each side is counted with the gap between boards on that side, and the second side has one fewer board. Horizontal fences use ⌈ (height + gap) ÷ (board width + gap) ⌉ rows, with one board per row per section. The picket calculator also reports the gap that spaces a whole number of pickets exactly:

even gap = (length − pickets × picket width) ÷ (pickets − 1)

Waste allowance

to buy = ⌈ exact quantity × (1 + waste % ÷ 100) ⌉

Waste applies to materials that are cut or can be defective: pickets, boards, rails, chain-link fabric and top rail. It is not applied to posts, concrete or pre-built panels.

Concrete

hole volume = π × (diameter ÷ 2)² × depth
post volume = width² × depth  (square) or π × (width ÷ 2)² × depth  (round)
bags = ⌈ (hole volume − post volume) × posts ÷ bag yield ⌉

The post is assumed to reach the bottom of the hole; a gravel base would reduce the concrete slightly. The typical bag yields used are:

The imperial figures are the yields commonly printed on U.S. pre-mixed concrete bags. The metric figures assume the same density, about 0.47 litres per kilogram. Products differ, and the bag you buy states its own yield.

Costs

The cost calculator multiplies each rounded quantity by a unit price, adds a per-section hardware allowance, gates, the cost of waste material, optional labor (a rate × total fence length, or a fixed amount) and optional tax (on materials, and on labor if you choose).

Prices vary by location and supplier, and change over time. The prices the calculator starts with are illustrative examples in U.S. dollars (reviewed September 2026), not market data or quotes. They are kept in a single configuration file so they can be reviewed and updated. Replace them with your own prices for a meaningful estimate.

Limits you should know about

• Structural design (post size, embedment depth, footing size, wind load) is not calculated.
• Slopes, stepped fences, curves and odd angles are not modeled; measure along the ground.
• Gate materials, post caps, fasteners, gravel and finishes are not counted in material lists.
• Lumber sizes are the common U.S. actual sizes unless you change them; check your supplier.

Testing

The formulas live in small, separate modules with automated tests covering typical fences, exact-fit cases, decimals, metric/imperial parity, very long fences, very small spacing, gates wider than the fence, invalid board sizes and rounding. If you find a case that looks wrong, please let us know.