Calculator
Example Data Table
| Item | Value |
|---|---|
| Shed size | 10 × 8 |
| Waste | 10% |
| Plank size | 48 × 8 |
| Planks / box | 10 |
| Layout | Straight |
Formula Used
Room Area: Σ(Length × Width × Quantity)
Openings: Σ(Length × Width × Quantity)
Net Area: Room Area − Openings
Final Area: Net Area × (1 + Extra%/100)
Plank Area: Plank Length × Plank Width (converted)
Planks: ceil(Final Area ÷ Plank Area)
Boxes: ceil(Planks ÷ PlanksPerBox)
Cost: Boxes × BoxPrice (optional)
How to Use
- Choose your measurement system.
- Add each garden area you’ll cover.
- Optionally subtract fixed openings.
- Enter plank size and box details.
- Set waste and trim allowances.
- Press calculate to see planks, boxes, and cost.
Planning Notes
Coverage planning for garden structures
Garden sheds, greenhouses, and potting studios often have mixed footprints with benches, drains, or staging shelves. This calculator totals each rectangular zone you enter, then subtracts fixed openings to produce a net coverage area. Splitting the space into smaller areas improves accuracy and reduces overbuying in tight garden rooms. It also helps when a walkway section uses different cuts than a storage corner, during seasonal reorganizations and upgrades.
Waste factors that change real ordering
Waste is not only about mistakes. Doors, tool alcoves, and irregular posts increase offcuts. Straight layouts commonly need 7–12% extra; diagonal patterns usually need more because many rows begin with cuts. Herringbone needs the most trimming and matching, so the tool adds a larger allowance. Keeping a spare box helps when batches change.
Plank sizing and box conversion
Plank coverage is calculated from the plank face dimensions, converted to your selected system. Required planks are rounded up to avoid shortages. Boxes are then calculated from planks-per-box, because cartons are sold as fixed quantities. If cartons list area coverage, set planks-per-box to match the label so ordering stays consistent. If you enter a box price, the tool multiplies it by the final box count for a quick budget.
Openings, built-ins, and thresholds
Subtract only permanent features that will not be floored, such as fixed soil stations, heavy planters, built-in cabinets, or drain channels. Do not subtract movable benches or rolling carts because their positions can change. For door thresholds and edge profiles, add a small trim allowance so reducers and transition pieces are covered.
Practical install checks for outdoor-adjacent rooms
Before ordering, confirm the subfloor is flat and dry, and plan acclimation time for boards in humid garden environments. Maintain expansion gaps at walls, especially in sun-warmed greenhouses. Consider entry mats near watering zones and verify underlayment compatibility with occasional dampness. The calculator’s final area is best used as your ordering target, while the breakdown tables support cutting plans and supplier discussions.
FAQs
What measurements should I enter for my garden shed?
Enter the interior finished dimensions where planks will be installed. Measure wall-to-wall, excluding skirting only if it will stay in place and you will stop short of it.
Should I subtract the area under movable benches?
No. Movable benches and carts can shift, and flooring them improves flexibility. Subtract only fixed, permanent features that will never be covered.
How do diagonal and herringbone allowances work?
The calculator adds an extra cutting percentage on top of your waste setting. Diagonal adds a smaller amount, while herringbone adds more because many pieces require trimming and matching.
Why does the tool round up planks and boxes?
Rounding up prevents shortages caused by partial coverage. You cannot buy fractions of a plank or a box, and small shortfalls typically cost more in delays and mismatched batches.
Can I use meters for rooms and centimeters for planks?
Yes. Choose the meters option and enter room dimensions in meters, with plank dimensions in centimeters. The calculator converts them to a consistent area unit.
When should I add a spare box?
Add one spare box when the space is high-traffic, humidity varies, or you want matching boards for later repairs. It is also wise when stock may be seasonal or limited.