Purple Martin House Calculator
Martin rooms, holes, and mounting height.
What it does
Purple martins nest colonially in human hung housing, returning yearly to good sites. Compartments, hole size, and height decide whether scouts stay or pass.
The tool above takes the target pair count. It returns compartments with spares, hole size, and mounting height in feet or meters.
The default 12 pairs needs 15 compartments at 2-1/8 in holes, set 12 to 18 ft high. The metric mirror reads 54 mm holes at 3.7 to 5.5 m.
Conservation guidance fixes 6 inch minimum rooms with starling resistant entries in open areas. Nesting references repeat the sizing with yearly cleaning.
Houses need landlords, not just hangers: open compartments on time, evict sparrows and starlings, and clean each fall for returning birds.
How to use
- Type target nesting pairs.
- Read compartments first.
- Read hole size beside it.
- Read mounting height last.
- Mount open near people.
- Clean each fall.
Formula
- pairs
- Target nesting pairs.
- rooms
- Rooms with 20% spare capacity.
Martin conservation guidance sets 6 inch minimum rooms with 2-1/8 inch entries at 12 to 18 ft in open areas. Bird nesting references mirror the same compartment sizing with fall cleaning. Counts plan housing; local insects set the real ceiling.
Worked example
Example: house 12 pairs
Imperial defaults: 12 nesting pairs.
- Colony: 12 nesting pairs targeted.
- Rooms: 12 x 1.2 = 14.4, up to 15.
- Holes: 2-1/8 in diameter, 6 in rooms.
- Mount: 12 to 18 ft high in open area.
- Care: clean compartments each fall.
- Tool shows 15 compartments, 2-1/8 in dia, 6 in rooms, 12 to 18 ft high, open area.
Reference table
| Pairs | Rooms | Holes |
|---|---|---|
| 12 | 15 | 2-1/8 in |
| 20 | 24 | 2-1/8 in |
| 6 | 8 | 2-1/8 in |
| 12 metric | 15 | 54 mm |
Limits
- Planning counts, not guaranteed birds.
- Insects limit real colonies.
- One region guidance generalized.
- Predator guards apart.
Common mistakes
- Tiny 4 in compartments.
- Low mounts near trees.
- Skipping fall cleaning.
- Ignoring sparrow takeovers.
- Late openings past scouts.
Try it yourself
Quick checks. Answers sit tucked under each question.
House 20 pairs?
20 x 1.2 = 24 compartments at the same holes.
House 6 pairs?
6 x 1.2 = 7.2, up to 8 compartments.
Zero pairs?
Below 1 is no colony: enter 1 to 200 pairs.
Questions
Rooms per pair?
Fifteen rooms for a dozen pairs with spares for bachelors and losses.
Hole size?
2-1/8 in round holes or starling resistant crescents, 6 in rooms minimum.
Mount where?
12 to 18 ft high in open areas near people, away from tall trees.
Why martins?
Colonial nesters that eat flying insects and return yearly to sites.
Clean yearly?
Yes, mites and sparrows compound in dirty cavities. Clean each fall.
Gourds differ?
No, houses host one colony while gourds hang arrays. Counts match either.