What it calculates
Estimate tank capacity from household and fixture demand.
Water Heater Sizing Planner
Estimate a tank-size range from household size and peak simultaneous use.
Planning and estimating aid only. Verify project requirements, manufacturer instructions, adopted codes, permits, and field conditions before performing regulated work.
Plumbing planning
How to Use This Calculator
Use the field units shown below, then compare your result with the worked example. Use actual fixture use and manufacturer sizing data for final equipment selection.
How the calculation works
The planner combines household size, peak showers and other estimated peak hot-water use to suggest a tank-size range.
What the result means
For final selection, compare peak-hour demand with the unit's first-hour rating and recovery performance.
Read the tool’s simple demand weighting
This tool assigns 8 gallons per entered person and 12 gallons per entered shower, then adds the Other gallons field. Two people and one shower therefore produce a 28-gallon arithmetic basis, which maps to 30 in its stored reference list.
Contractor tip: Use actual fixture use and manufacturer sizing data for final equipment selection. Do not assume the displayed tank-volume reference can meet the household’s actual demand.
Verify the final quantity
Those weights are a simplified heuristic, not a verified peak-hour profile or an equipment recommendation. A tank’s volume is different from its first-hour delivery, and recovery rate, inlet temperature and use patterns matter.
Good practice: Compare the calculated quantity with plans, specifications, product packaging and current field conditions before purchasing material.