Shower Pan Slope Calculator: enter horizontal run to the drain and choose pitch. Formula: required drop = run × slope ratio. Outputs drain drop, grade, level checks, and mud bed checkpoints for a pan.
Enter the horizontal distance from the furthest wall to the center of your drain, select a pitch target, and this calculator returns the exact vertical drop your mud bed must achieve — plus span checkpoints for verifying slope with a level and tape during installation.
Why Shower Pan Slope Is a Structural Requirement, Not a Preference
A shower pan that does not drain fully between uses creates a reservoir of standing water against the liner and subfloor. Over time, even a continuous 1/16″ pool accelerates liner degradation, wicks into surrounding framing, and creates persistent anaerobic conditions that breed mold inside the wall cavity — damage that is invisible until it is expensive. The slope requirement exists precisely because a properly pitched pan dries between uses. A flat one does not.
Beyond moisture, slope affects user safety. A floor that drops too steeply — above 1/2″ per foot — becomes a slip hazard on wet, soapy tile. The standard pitch window of 1/4″ to 1/2″ per foot is not arbitrary: it represents the tested range where water sheds to the drain fast enough to prevent pooling but not so fast that the floor angle creates instability underfoot.
The Formula This Calculator Uses
The calculation is linear. The total vertical drop from any point on the shower floor to the drain flange equals the horizontal run multiplied by the slope ratio:
$$\text{Total Drop (inches)} = \text{Horizontal Run (inches)} \times \frac{\text{Pitch (in/ft)}}{12}$$
For the standard 1/4″ per foot pitch, the ratio reduces to:
$$\text{Ratio} = \frac{0.25}{12} = 0.02083$$
So a shower with a 36-inch run to the drain requires:
$$36 \times 0.02083 = 0.75 \text{ inches of total drop}$$
The mud bed at the perimeter must sit exactly 3/4″ higher than the top of the drain flange. That is the only number that matters when you are setting your screed guides.
The calculator also converts this ratio into a 1:N slope expression and a degree angle for situations where plans or inspectors specify slope in those terms, and it outputs drop values at fixed spans (24″, 48″, 72″) so you can verify your pitch with a straightedge and tape rather than relying on a digital level alone.
Accepted Shower Pan Pitch Standards
The following pitch thresholds are referenced across the major tile and construction standards used in North America. Always verify against your local adopted building code, as jurisdictions may amend these figures.
| Pitch Rate | Ratio | % Grade | Status | Notes |
|---|---|---|---|---|
| 0″ / ft | 1:∞ | 0% | Fail | Guarantees standing water. No liner or drain system compensates for zero slope. |
| 1/8″ / ft | 1:96 | 1.04% | Conditional | Accepted only in ADA roll-in shower designs with specific drain placement. Not suitable for standard showers. |
| 1/4″ / ft | 1:48 | 2.08% | Standard Minimum | The baseline slope for mud-set shower pans per TCNA guidelines and most residential codes. |
| 3/8″ / ft | 1:32 | 3.13% | Acceptable | Often used with large-format tile to maintain pitch across a longer run without excessive perimeter height. |
| 1/2″ / ft | 1:24 | 4.17% | Standard Maximum | Upper limit for comfort and tile layout. Above this, grout joints and tile faces begin to read as visibly angled. |
| >1/2″ / ft | <1:24 | >4.17% | Not Recommended | Creates a noticeable and potentially hazardous slant on a wet surface. |
How to Use the Calculator
Step 1 — Measure the Horizontal Run
Measure from the center of the drain to the furthest point of the shower floor — typically the back wall or the farthest corner. Do not measure to the nearest wall. The run determines the maximum drop your mud bed must achieve, and the furthest point sets that number. If your drain is not centered, calculate each quadrant separately and use the largest run to ensure full coverage.
Enter this measurement in inches, feet, meters, centimeters, or millimeters depending on your workflow. The calculator handles the conversion internally.
Step 2 — Select Your Pitch Target
For most standard mud-set shower pans, use 1/4″ per foot. Select the 1/2″ preset if you are building a very small shower (under 24″ run) where the absolute drop at 1/4″ per foot would be less than 1/2″ — a shallow target that is difficult to hold in mortar. The custom pitch option accepts any value in inches per foot, millimeters per meter, or percent grade for situations where an engineer or waterproofing system specifies an exact slope.
Step 3 — Read the Results
Total Required Drop — This is the number you need when setting your perimeter screed guides. The drain flange sits at your finished floor elevation. The mud bed at the wall side of the pan must be this many inches (or millimeters) higher than that flange surface.
Slope Equivalents — The 1:N ratio and degree angle are useful if your project documents express slope differently. A 1/4″ per foot pitch equals a 1:48 ratio and a 1.19° incline. These are the same slope described three different ways.
Drop per Span — These values let you verify slope during installation without relying on a digital tool. If your pitch is 1/4″ per foot, a 4-foot straightedge resting on the pan should show a 1.00″ gap at the high end when the low end is at the drain. The calculator outputs this for 24″, 48″, and 72″ spans (or 60cm, 120cm, 180cm in metric mode) so you can pick whichever span your straight edge accommodates.
Mud Bed Checkpoints — These are the vertical drop values at 25%, 50%, and 75% of your total run. Use them to verify that your mud bed slope is linear — not humped in the middle or steeper near the drain — which would cause water to pool at the transition zone.
Verifying Slope During Mud Bed Installation
Calculating the correct drop is only useful if you can verify it in the field. There are three reliable methods:
Straightedge and Tape
This is the most precise method for mud beds. Place a known-length straightedge on the pan surface with one end touching the drain flange rim. Measure the gap at the other end with a tape measure. Compare this gap to the “Drop per Span” value from the calculator for that straightedge length. If the gap matches within 1/16″, your slope is set correctly at that line. Check at least four radial lines from drain to wall to confirm consistent slope in all directions.
Digital Level with Known Span
A digital level reads slope as a percentage or degree. For 1/4″ per foot pitch, you are targeting 2.08% or 1.19°. Set the level on a straightedge long enough to span at least 24″ of the pan. The reading should be consistent across multiple radial positions. This method works well for pre-slope checks before the liner goes down.
Screed Guide Pins
Set screed guide pins at the drain elevation (zero) and at the perimeter elevation (total required drop from the calculator). Strike off the mortar bed to these pins. After striking, use the straightedge-and-tape method at the quarter-run checkpoints from the calculator to verify the surface is planar between the pins — mortar can slump or settle unevenly during compaction.
Slope Considerations for Large-Format Tile
Large-format tile (any tile with at least one edge longer than 15 inches) introduces two slope-related problems that smaller format tile does not have.
First, a single large tile must bridge a greater elevation change across its face. At 1/4″ per foot on a 24″ tile, the tile face drops 1/2″ from back to front. The tile must be fully supported across this entire lippage — not just at the edges — which requires a thicker mortar bed or a back-buttered skim coat to fill the low void.
Second, large tiles make it harder to follow a curved drain-slope profile. The TCNA recommends that the slope be established in the mud bed, not corrected by varying mortar thickness under individual tiles. If your mud bed slope is not accurate, large-format tiles will rock or crack under foot traffic as they bridge uneven low spots.
For large-format tile, a 3/8″ per foot pitch is often a better target than 1/4″. It provides a meaningful drainage gradient while keeping the visible face-angle of each tile within an acceptable visual range. Use the custom pitch field to enter 0.375 in/ft and recalculate your drop targets.
Off-Center Drains and Multi-Slope Pans
This calculator assumes the drain is at or near the center of the shower floor, which produces equal runs in all directions. If your drain is positioned against one wall — as in a linear drain installation — each side of the pan has a different horizontal run and therefore a different total drop calculation.
For an off-center drain, run the calculator separately for each distinct run:
- Measure and calculate the short run (drain to nearest wall). This gives you the drop target for the shallow side of the pan.
- Measure and calculate the long run (drain to furthest wall). This gives you the drop target for the deep side of the pan.
- Set your perimeter guides independently for each wall based on its respective calculated drop.
Linear drain installations along one wall simplify this — the entire pan slopes in one direction, making the run a single dimension from the back wall to the drain. Enter that full dimension as your run and use the standard 1/4″ per foot pitch. The linear drain manufacturer’s installation guide may specify a minimum slope; always check this against your calculated value.
Frequently Asked Questions
What happens if I build the slope slightly steeper than 1/2″ per foot?
Water drainage will not be the problem — a steeper slope drains faster. The problem is comfort and safety. A slope above 1/2″ per foot is perceptible underfoot and becomes increasingly uncomfortable in bare feet on a wet surface, especially for older users or anyone with balance considerations. Above 3/4″ per foot, the floor becomes a genuine slip hazard that wet tile and soapy water make worse. If your shower is unusually small and the total drop at 1/4″ per foot is less than 3/8″ total — which can happen in a 24″ run — the 1/2″ per foot setting produces a total drop of just 1/2″ over 24 inches, which is still within the safe comfort range.
Does the pre-slope under the liner need to match the finished floor slope?
Yes. The pre-slope (the mortar bed installed below the liner) must achieve the same pitch as the finished surface. Its purpose is to drain any water that migrates through the liner to the weep holes at the drain base. A flat pre-slope with a correctly pitched finished surface means any liner leak pools against the liner indefinitely rather than weeping to the drain. Calculate the slope for the pre-slope using the same run and pitch as the finished floor, but measure to the sub-drain weep holes rather than the finished drain flange elevation.
My shower floor is 60 inches by 36 inches with a centered drain. Which run do I use?
Use half of each dimension, since the drain is centered. The run in the long direction is 30 inches (half of 60″). The run in the short direction is 18 inches (half of 36″). Calculate both. The 30-inch run produces the larger total drop — that is your critical target for the furthest perimeter point. The 18-inch sides will naturally meet their smaller drop requirement if the bed is screeded consistently to the same pitch throughout. Use the mud bed checkpoints for the 30-inch run to verify the slope is linear across the full length of the pan.
Can I build slope into a membrane-only system instead of a mud bed?
Sheet-applied and liquid waterproofing membranes (Schluter Kerdi, WEDI, Laticrete Hydro Ban Sheet) installed directly over a sloped substrate rely on that substrate for their pitch — the membrane itself is thin and conforms to whatever is beneath it. You still need to establish the correct slope either in a mortar pre-slope, by using a manufacturer-supplied prefabricated sloped shower tray, or by pouring a self-leveling underlayment over a pre-sloped substrate. The total drop calculation from this tool applies regardless of which waterproofing system you use.
The calculator shows my total drop is only 3/8 of an inch. Is that achievable in a mud bed?
It is achievable but difficult to maintain during compaction. Mortar beds compress and shift as you tamp them, and a 3/8″ total drop over a short run leaves almost no room for error at the screed stage. In very small showers, some installers increase the pitch to 3/8″ per foot rather than 1/4″ per foot to produce a larger absolute drop that is easier to hit consistently. Re-run the calculator with 0.375 in the custom pitch field to see what total drop that yields for your specific run.
What is the 1:48 ratio figure in the results?
It means the floor rises 1 unit vertically for every 48 units of horizontal distance. At 1/4″ per foot, one inch of vertical rise occurs over 48 inches (4 feet) of horizontal run. This is the same slope expressed as a dimensionless ratio, which is the format used in architectural drawings and some accessibility guidelines. The ADA slope standard for accessible surfaces is 1:48 maximum — which is exactly the shower pan minimum. This is not a coincidence: the minimum drainage slope for a shower happens to coincide with the maximum cross-slope permitted for accessible routes, which is why roll-in showers sometimes specify 1/8″ per foot (1:96) instead to remain accessible while still shedding water.
Disclaimer: This calculator is provided for general estimation purposes. Always verify slope requirements against your local plumbing code, building code, and the Authority Having Jurisdiction (AHJ) in your area before finalizing a shower installation. Code requirements vary by municipality and may differ from the UPC and IRC guidelines referenced here. For accessible and ADA-compliant designs, consult a licensed contractor or accessibility specialist.
Last reviewed: 2026 — references UPC (8th Ed.), IRC (2021), ANSI A117.1-2017, and TCNA Handbook current edition.