Choose units and a shape. The layout adapts to your screen.
The calculator places anchors evenly along each edge, including both ends.
- Anchors per edge = ceil(edge_length / spacing) + 1
- Total (raw) = 2 × long_edge + 2 × short_edge
- Total (unique) = Total (raw) − 4 when corners are shared
- Spares = ceil(total_unique × spare_percent / 100)
For irregular shapes, anchors are estimated from the perimeter: ceil(perimeter / spacing).
- Select your unit system and choose a shape.
- Measure the cover footprint or perimeter carefully.
- Set anchor spacing based on strap locations.
- Decide whether corners share a single anchor.
- Add spare percentage for lost or damaged anchors.
- Press Submit to view results above the form.
- Use CSV or PDF exports for planning and ordering.
Sample scenarios to sanity-check your settings.
| Scenario | Shape | Size | Spacing | Corner share | Estimated anchors | Spares (10%) |
|---|---|---|---|---|---|---|
| Garden pond cover | Rectangle | 12 ft × 8 ft | 18 in | Yes | 38 | 4 |
| Small pool winter cover | Rectangle | 20 ft × 12 ft | 24 in | Yes | 32 | 4 |
| Irregular water feature | Custom perimeter | Perimeter 18 m | 45 cm | — | 41 | 5 |
Anchor planning for safer cover installs
Accurate anchor counts reduce trip hazards, loose edges, and wasted drilling. This calculator converts your measured footprint into a repeatable hardware plan. For rectangles, it places anchors at both ends of each side and then distributes the remaining anchors evenly. The output includes per‑edge counts, an average realized spacing, and a purchasing total that already includes your chosen spares. Use exports to share counts with suppliers, track jobs, standardize layouts across seasons, and ensure installation follows the same measured, documented approach from start through finish.
Spacing selection and strap alignment
Spacing drives performance more than any other input. Smaller spacing increases holding points and reduces edge lift, while larger spacing reduces drilling and labor. Choose a spacing that matches strap loops or webbing locations on the cover, then verify that the computed actual spacing stays close to your target. If the actual spacing is wider than expected, reduce spacing or recheck measurements.
Corner sharing and overlap logic
Corners often use one shared anchor because two edges meet at the same point. When corner sharing is enabled, the rectangle method subtracts four duplicates from the raw perimeter sum. This prevents double‑counting anchors that physically occupy the same corner position. If your cover design uses separate corner straps or offset loops, disable corner sharing to reflect two independent anchor points.
Spare anchors and field realities
Real projects lose hardware to debris, corrosion, and seasonal removal. A spare percentage creates a buffer for damaged inserts, stripped holes, or misplaced bolts during installation. Many crews keep 5–15% spares on hand; higher percentages make sense for rocky borders or mixed materials. The calculator rounds spares up so you never fall short by a fraction.
Custom perimeter option for irregular shapes
For curved ponds, kidney beds, and irregular water features, measuring a full perimeter is faster than modeling multiple sides. Enter the perimeter and the calculator estimates anchors as perimeter divided by spacing, rounded up. The result reports an average spacing that helps you mark positions with a tape and chalk. For best accuracy, measure along the real anchoring line, not the water edge.
FAQs
How many anchors should I add as spares?
A common buffer is 5–15% depending on material and seasonal handling. Use a higher spare rate for rocky borders, mixed substrates, or when anchors are removed and reinstalled frequently.
Why does the rectangle method add one anchor per edge end?
It assumes anchors at both ends of each edge for secure corner control. The remaining anchors are then distributed between ends based on your spacing, producing a practical layout for marking and drilling.
When should I disable corner sharing?
Disable it if your cover uses separate corner straps, offset loops, or hardware that cannot share a single hole. In that case, counting corners twice better reflects two distinct anchor points.
Can I use this for irregular pond shapes?
Yes. Choose the custom perimeter option and enter the measured perimeter along the anchoring line. The calculator estimates anchors by spacing and reports an average spacing to guide field marking.
What measurements give the best accuracy?
Measure the footprint where anchors will be installed, not the water edge. For borders with curves, follow the true drilling path with a flexible tape to avoid undercounting perimeter length.
Do the exports include my notes and settings?
Yes. CSV and PDF exports include the chosen units, shape, spacing, spare rate, and any job notes you entered, so you can share a consistent plan with suppliers or your crew.
Tip: If your cover has fixed strap loops, use that spacing.