Introduction
Every cedar project — a privacy fence, a deck, a siding job, a pergola — starts with the same question: how much cedar do you actually need? Order too little and the job stalls while you hunt for matching boards; order too much and you pay for premium lumber you don’t need. Cedar estimating answers that question with arithmetic: measure the structure, convert it into boards using actual (not nominal) dimensions, and add a waste allowance that fits the grade.
The Cedar Lumber Calculator handles the core calculation: enter your project dimensions, board size, and waste allowance, and it returns board counts, linear feet, and board feet in both metric and imperial units. This guide explains everything behind that number — the terminology, the formulas, a full worked example, and the judgment calls the calculator can’t make for you, such as which grade belongs on a fence versus a deck.
What Cedar Estimating Covers
Cedar is estimated the same way regardless of the project — surface area or linear run, converted into boards — but each application has its own layout math. The four projects that drive most cedar orders:
- Fences: linear feet of run converted into pickets (picket width plus gap), plus posts at regular spacing and horizontal rails.
- Decks: deck area converted into linear feet of decking with a coverage factor, plus framing lumber for joists, beams, and posts.
- Siding: wall area (minus major openings) converted into boards, where overlap and exposure change the math.
- Pergolas and arbors: counted piece by piece — posts, beams, rafters, purlins — from a cut list rather than an area formula.
Western red cedar is the species behind nearly all of this work — light, naturally rot-resistant, and the reason careful estimating pays. The material guide compares it with incense and Alaskan yellow cedar and explains the grade ladder from clear heart down to knotty stock.
Key Terms and Variables
The calculator moves between these units — getting the vocabulary right is half the battle:
Board feet
One board foot = 144 cubic inches. Formula: (thickness in inches × width in inches × length in feet) ÷ 12. A nominal 2×6×8 board is 2 × 6 × 8 ÷ 12 = 8 board feet.
Linear feet
The total length of boards end to end, regardless of width. Decking, fencing pickets, and trim are usually ordered by the linear foot. A 100-foot fence of 6-foot pickets needs roughly 1,200 linear feet of picket stock before waste.
Nominal vs. actual dimensions
The single biggest source of estimating error. A “1×6” is not 1 inch by 6 inches — surfaced, it measures 3/4 in × 5-1/2 in (19 mm × 140 mm). Always estimate with actual dimensions — the face width of the board, not its nominal name.
Grade
Cedar’s appearance grading: clear heart (knot-free), A & Better (near-clear), STK (select tight knot), and #2 / common. Grade drives price and waste: knotty grades need a bigger cutting allowance because you cut around defects.
Waste %
The allowance added for cutting losses, defects, and end-trimming. Cedar-specific guidance:
| Situation | Suggested waste allowance |
|---|---|
| Clear grades, straight runs (deck field, siding) | 5–10% |
| Typical residential fence or deck, STK grade | 10% |
| Knotty grades, cutting around defects | 10–15% |
| Complex layouts, pergolas, many short cuts | 15% |
The formula guide works through how waste compounds with board counts.
The Core Formulas
Every cedar estimate is a variation on three calculations:
- Boards = coverage length ÷ (board face width + gap). For a fence, the run length divided by picket width plus spacing. For a deck, the deck width divided by decking face width plus gap.
- Linear feet = boards × board length. Total material in one dimension.
- Order quantity = linear feet × (1 + waste %), rounded up to whole boards.
For decking there is a handy shortcut: deck square footage × 2.2 ≈ linear feet of 5/4×6 decking (face plus gap included — add waste on top). In metric, multiply square meters by about 7.2.
Worked Example: A 100-Foot Cedar Fence
A privacy fence 100 ft (30.48 m) long and 6 ft (1.83 m) tall, built with 1×6 pickets (5-1/2 in / 140 mm actual face) and a 1/4 in (6 mm) gap, posts every 8 ft, two rails per bay, 10% waste:
Pickets: 100 ft = 1,200 in; each picket covers 5.5 + 0.25 = 5.75 in. 1,200 ÷ 5.75 = 208.7 → 209 pickets. At 6 ft each: 209 × 6 = 1,254 linear feet before waste.
Waste: 1,254 × 1.10 = 1,379.4 → 1,380 linear feet, or 230 six-foot pickets.
Posts and rails: 100 ÷ 8 = 12.5 bays → 13 bays → 14 posts (4×4×8); rails: 2 per bay × 13 = 26 rails (2×4×8, 208 linear feet).
Cross-check in metric: 30.48 m ÷ 0.14605 m per picket = 208.7 → 209 pickets × 1.83 m = 382.5 m; × 1.10 = 420.7 m, matching 1,380 ft × 0.3048 = 420.6 m.
For a step-by-step version of this exact estimate, see the estimating guide; pricing it out is covered in the cost guide.
Cedar Grades and Where They Belong
Grade selection is an estimating decision — it changes the waste factor and the unit price:
- Fences: STK (select tight knot) is the sweet spot — attractive, affordable, and defects are easy to cut around at 10% waste.
- Decks: A & Better or STK for decking; tighter grades mean fewer weak spots underfoot. Clear is a luxury upgrade.
- Siding: clear or A & Better for the face; knots bleed and check over time on exteriors.
- Pergolas: STK or #2 structural where appearance matters less; posts and beams are often rough-sawn.
Buying clear grade for a fence is the classic overspend — the knots you paid to avoid add nothing at viewing distance. The reverse (knotty siding) is the classic underbuy.
Mistakes That Distort Results
Most cedar estimating errors are not arithmetic — they are wrong inputs and wrong assumptions:
- Using nominal dimensions. Estimating a fence with 6-inch pickets instead of 5.5-inch actual faces understates the count by about 8%.
- Forgetting the gap. Decking and fence pickets need spacing for drainage and movement; zero-gap math undercounts boards.
- One waste factor for every grade. Knotty stock at 5% waste guarantees a second trip to the yard.
- Counting the run, not the bays. Posts sit at bay ends — a 100 ft fence at 8 ft spacing needs 14 posts, not 12.5.
- Ignoring the finish and fasteners. The lumber number is only part of the project cost; stainless fasteners and stain belong in the budget from the start.
The common mistakes guide catalogues these in full, including the iron-stain problem that ruins more cedar than bad math does.
Related Guides
- Cedar Lumber Calculator FAQ — quick answers to the most asked cedar estimating questions.
- Formula Explained — the full derivation of board counts, linear feet, and waste.
- Material Guide — cedar species, grades, and rough vs. surfaced stock.
- Cost Guide — cedar vs. pressure-treated vs. composite pricing and project budgets.
- Pro Tips — buying, acclimation, fasteners, and finishing schedules.
- Pre-Order Checklist — everything to verify before you place the lumber order.
Frequently Asked Questions
How many pickets do I need for a 100-foot cedar fence?
About 209 six-foot 1×6 pickets (5-1/2 in face, 1/4 in gap): 1,200 in ÷ 5.75 in = 208.7, rounded up. That is 1,254 linear feet before waste; with 10% waste, order 230 pickets (1,380 linear feet).
What is the formula for estimating cedar decking?
Linear feet ≈ deck square footage × 2.2 for 5/4×6 decking with a 1/4 in gap, then multiply by (1 + waste %). In metric, multiply square meters by about 7.2.
How much waste should I add for knotty cedar?
Plan 10–15% for STK and knotty grades, since you will cut around knots and defects. Clear grades can run 5–10% on straight layouts.
Do I use nominal or actual board dimensions?
Actual. A 1×6 picket covers 5-1/2 inches of face, not 6. Using nominal widths understates board counts by roughly 8%.
What grade of cedar should I use for a fence?
STK (select tight knot) is the standard choice — good appearance at a moderate price, with defects easy to trim around at a 10% waste factor.
Get Your Number
Cedar estimating is straightforward once the inputs are honest: actual board dimensions, real gaps, a grade-appropriate waste allowance, rounded up to whole boards. The Cedar Lumber Calculator does the arithmetic — your job is the tape measure and the grade decision.
Disclaimer: Calculator results are planning estimates based on the dimensions you enter. Actual material needs vary with site conditions, product availability, and local pricing. Verify quantities with your supplier and consult a licensed professional for structural or code-related decisions.
