Bathroom
Shower Pan Size Calculator
Calculates shower pan dimensions for typical shower stalls
Updated May 13, 2026 · Live
What this tool does
Calculates shower pan dimensions for typical shower stalls.
Calculates shower pan width and depth from alcove dimensions, accounting for standard fit clearance.
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Formula Used
How the shower pan size calculator works
Calculates shower pan dimensions for typical shower stalls. The calculator takes your dimensions and supplier rates, applies a standard US construction formula, and returns a quantity with an indicative cost. Every figure is an estimate — site conditions always move the final number.
Typical US bathroom wastage
Tile runs 10–15% wastage around tubs, showers, and complex layouts. Whole boxes are typically ordered, since partials are usually non-returnable. Our defaults reflect common US trade allowances, and can be adjusted upwards for non-standard geometry or downwards where experience supports a lower figure.
What this tool does not do
It does not replace a professional quote, factor regional pricing, assess structural adequacy, or confirm building code compliance. Those remain the responsibility of a suitably qualified designer, engineer, or your local building official.
On-site considerations for shower pan size
Wet rooms (curbless showers) need correct slopes (1/4" per ft minimum), an impervious substrate, and the right drain type. Flexing OSB or plywood floors crack tile grout — overboard with cement-board (Hardiebacker, Durock) before tiling.
Codes and compliance
Bathrooms in new construction follow the IRC, IPC, and NEC. GFCI protection on receptacles, dedicated 20-amp circuit, and ventilation per IRC R303.3 (50 CFM intermittent or 20 CFM continuous) are code minimums. When in doubt, file a pre-application question with your local building department — early clarity is cheaper than a corrective inspection.
Before you order
Order fixtures and trim together — tile layout depends on wall-hung toilet and vanity rough-in heights, not the other way around. Cross-checking the calculator’s output against a supplier quote helps catch differences in pricing assumptions — ask for exact product specifications (grade, finish, batch number) and confirm delivery timescales against your programme.
Adjusting the defaults
Every input in this calculator is editable. Enter your own dimensions, supplier prices, and wastage allowance — the output recalculates instantly. If the defaults feel off for your region or project type, your own numbers always override them.
Using this shower pan size calculator alongside other BuildMetricLab tools
This calculator works best as part of a planning workflow. Pair the quantity with our project contingency, labor-hours, and material-cost calculators to build a complete estimate before you pick up the phone to a supplier. All BuildMetricLab tools run entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the math.
Sources & methodology
This tool calculates the target dimensions of a prefab shower pan from the alcove measurements entered by the user. It applies a fit-clearance deduction on both sides of each dimension: pan width equals alcove width minus twice the clearance value, and pan depth equals alcove depth minus twice the clearance value. This accounts for out-of-plumb walls and installation tolerance common in prefab shower pan installations. Always confirm the exact clearance recommended by your specific shower pan manufacturer before cutting or ordering.
Frequently asked questions
Are shower pan size calculator results accurate enough to order materials?
Use them as a starting estimate only. Verifying the final quantity with your supplier or contractor before ordering is good practice — site conditions, wastage and cut-offs all affect the true figure.
How much fit clearance should I allow?
A fit clearance of about 0.25 in (0.0625–0.25 in typical) per side is common for prefab shower pans to accommodate slightly out-of-plumb framing and finish tolerances. Check your specific pan manufacturer's installation instructions, as required clearance can vary by product.
Does this replace professional advice?
No. This tool is a planning estimator. For work that affects structure, building code compliance, gas, electrical, plumbing, or drainage to a public sewer, consult a licensed contractor or design professional.
Can I use this for corner or neo-angle shower pans?
This calculator is designed for rectangular alcove shower pans measured by width and depth. Corner and neo-angle pans use different sizing conventions and are not covered by this tool.
Spotted something off?
Calculations or display — let us know.
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