Calculator
Use this for garden rooms, patios, and indoor-outdoor walls where reflections expand space. Enter wall size, margins, and either wall or furniture sizing rules.
Formula used
- Usable wall width: usable_w = wall_w − 2 × side_margin
- Target width (wall method): target_w = usable_w × (coverage ÷ 100)
- Target width (furniture method): target_w = furn_w × (furn_ratio ÷ 100)
- Aspect ratio: choose width/height ratio (w_over_h)
- Target height: target_h = target_w ÷ w_over_h
- Max available height: max_h = (wall_h − top_margin) − (furn_h + clearance) when furniture height is provided
- Clamp: recommended sizes are clamped to user min/max and wall constraints
- Area coverage: (mirror_area ÷ wall_area) × 100
How to use this calculator
- Measure wall width and height where the mirror will hang.
- Set side and top margins for trim, beams, or planters.
- Pick wall coverage, or switch to furniture-based sizing.
- Select an aspect ratio that matches the design style.
- Add frame thickness to preview overall outer dimensions.
- Press calculate, then download CSV or PDF if needed.
Tip: In garden rooms, avoid placing mirrors where direct sun can reflect into seating areas.
Example data table
| # | Wall (W×H) | Method | Target width | Aspect | Recommended mirror | With frame |
|---|---|---|---|---|---|---|
| 1 | 72×84 in | Wall 65% | 39.0 in | 4:5 | 39×48.75 in | 42×51.75 in |
| 2 | 60×96 in | Furniture 70% | 42.0 in | 2:3 | 42×63 in | 45×66 in |
| 3 | 90×90 in | Wall 60% | 46.8 in | 1:1 | 46.75×46.75 in | 49.75×49.75 in |
Examples illustrate typical outputs; your result depends on margins, clearances, and limits.
Sizing targets for garden walls
Most wall mirrors look balanced when the glass width lands between 55% and 75% of the usable wall width. “Usable” means the wall width minus both side margins, trim, posts, or planting ledges. For safety, keep mirrors away from direct sprinkler spray, and use corrosion-resistant fixings; moisture and fertilizer salts can stain edges over time quickly in summer. For narrow garden rooms, starting at 60–65% keeps edges clear and reduces glare hotspots.
Clearances and margins
Top margin protects the mirror from beams, outdoor-rated light fittings, and ceiling transitions. If a console, bench, or potting shelf sits below, the clearance above it preserves breathing space and helps avoid bump damage. A common starting clearance is 8–12 units, letting décor, hooks, and watering cans sit comfortably below. When furniture height is entered, the calculator limits mirror height to maintain the chosen top margin and the clearance zone.
Choosing an aspect and shape
Aspect ratio controls how “tall” the mirror reads. Portrait ratios (4:5 or 2:3) add vertical lift and often suit doorways or slim wall bays. Landscape ratios emphasize width and can visually widen a patio wall. If you want more reflection of plants than people, choose landscape ratios and mount slightly lower. Round and arched options soften hard edges, which works well near planting textures and stonework.
Frame allowance and sourcing
Glass size and overall outside size are different. The frame thickness is added on both sides to estimate the full footprint on the wall. This helps with sourcing, because retailers may list overall dimensions while installers work from glass or backing size. A consistent frame also improves durability in humid garden rooms.
Reading the results and exporting
The result panel reports recommended glass dimensions, overall framed size, maximum available height, and area coverage. Area coverage is a useful check: a mirror that covers 12–20% of wall area usually feels intentional without dominating. Export CSV for quick quotes, and export PDF to share measurements with installers.
FAQs
1) What if my wall has a window or trellis?
Measure only the clear wall section where the mirror will sit, then set side and top margins so the mirror does not overlap the obstacle. The usable width field reflects those margins.
2) Which method should I use: wall or furniture?
Use wall coverage when the mirror is the main wall feature. Use furniture-based sizing when a console, bench, or potting shelf anchors the layout and you want the mirror to relate to that width.
3) How do I avoid glare in bright sun?
Increase side margins, reduce coverage slightly, and choose softer shapes or wider frames. In outdoor-facing rooms, angle placement away from direct sun paths and avoid reflecting into seating lines.
4) Why did the calculator change my aspect ratio?
If height or width constraints are tight, the tool fits the mirror within limits while trying to preserve your chosen ratio. Adjust margins or max limits to keep the ratio closer.
5) What frame thickness should I enter?
Enter the visible frame thickness on one side. For example, a 4 cm frame adds 8 cm to overall width and height. If you have a backing board, include that extra border too.
6) Is area coverage more important than width coverage?
Width coverage drives first impressions and symmetry, while area coverage checks overall dominance. Use both: start with 55–75% width, then confirm the area percentage aligns with the wall’s visual weight.