| Length (in) | Width (in) | Drain X (in) | Drain Y (in) | Slope (in/ft) | Drain Thickness (in) |
|---|---|---|---|---|---|
| 60 | 36 | 30 | 18 | 0.25 | 1.00 |
| 48 | 48 | 24 | 24 | 0.25 | 1.25 |
| 72 | 42 | 18 | 21 | 0.30 | 1.00 |
1) Distance from drain to any point
Distance
d = √((x − dx)² + (y − dy)²)
2) Rise based on slope rate
Rise
rise = (d / 12) × slope
(slope is inches per foot)
3) Thickness at that point
Thickness
thickness = drain_thickness + rise
- Choose your unit system and enter pan length and width.
- Measure the drain position from the top-left corner.
- Enter the slope rate and your drain thickness target.
- Click Calculate Slope to view corner and edge heights.
- Use the maximum thickness to set perimeter screed marks.
- Export CSV or PDF to share measurements with the crew.
1) Why slope consistency matters
Standing water stains grout, increases slip risk, and shortens waterproofing life. A uniform fall to the drain keeps flow predictable and reduces “birdbaths” after tile is set. This calculator converts a chosen slope rate into perimeter height targets you can verify with a straightedge.
2) Practical slope targets used in the field
A common target is 0.25 inches per foot, producing drainage without an uncomfortable pitch. Faster slopes may suit high‑flow areas, while slower slopes can trap water. Enter your rate and compare maximum rise against framing, curb, and threshold limits.
3) Drain position changes every perimeter height
Centered drains keep corner thicknesses closer together. Offset drains create a farthest corner that drives maximum rise and may require curb adjustments or recessed framing. The “farthest point” row highlights the worst‑case build‑up you must accommodate.
4) Mortar bed thickness planning at the flange
Drain thickness is the starting point. Adding the calculated rise yields thickness at corners and mid‑edges. If you set a minimum perimeter thickness, the tool suggests a drain thickness that keeps the farthest perimeter at or above target, avoiding weak feather‑thin edges.
5) Layout workflow for screed guides
Mark perimeter elevations first, then pull screeds toward the drain. Use the corner and mid‑edge values as checkpoints, and add intermediate points on long runs. Measure from the same reference corner to prevent transfer errors across studs or backer board.
6) Waterproofing and tile assembly considerations
Membranes and bonded systems depend on stable slope. Confirm your mortar thickness meets manufacturer minimums and supports the drain assembly. Small mosaics tolerate steeper changes; large-format tile needs flatter transitions and careful perimeter leveling.
7) On‑site checks that reduce callbacks
Before waterproofing, correct low spots while material is workable. After placement, verify heights with a level and tape at multiple radii. Consistent slope percent around the perimeter is more reliable than a single check at one corner. Use a straightedge from perimeter marks to the drain to confirm a plane and correct any humps immediately before waterproofing cures.
8) Documentation for crew handoff and inspection
Export CSV or PDF and attach it to the job packet. Record units, slope rate, drain thickness, and farthest‑point thickness. Clear numbers help installers set guides quickly and give inspectors objective confirmation of drainage intent and workmanship quality.
1) What slope rate should I start with?
Many installers begin with 0.25 inches per foot because it drains well without feeling steep. Adjust if your system, tile size, or local requirements call for a different rate.
2) How do I measure drain position correctly?
Measure from the same reference corner used by the calculator: X from the left edge and Y from the top edge. Keep units consistent and measure to the drain centerline.
3) Why are the corner thickness values different?
Thickness depends on distance to the drain. If the drain is off-center, the farthest corner needs the most rise, so it ends up thicker than the nearest corner.
4) What does “drain thickness at flange” mean?
It is the mortar thickness directly at the drain where the bed meets the drain assembly. The calculator adds rise to this value to estimate thickness at each perimeter point.
5) Can I use centimeters or millimeters?
Yes. Choose your preferred unit for inputs and outputs. The slope rate stays in inches per foot because it is a common field convention, but rises and thicknesses are displayed in your selected unit.
6) Does this replace manufacturer instructions?
No. Use it for planning and verification, then confirm minimum thickness, drain details, and waterproofing steps with your product documentation and applicable code requirements.
7) How do I use the results on site?
Transfer the corner and mid-edge thicknesses to perimeter marks, build screeds, and pull toward the drain. Recheck with a straightedge and level, then export CSV or PDF for records.