Two showers GPM?
About 5.0 GPM from showers alone (2 × 2.5).
Enter how many showers and sinks run at once, optionally mark dishwasher/washer running, and set temperature rise in °F.
Primary output is peak hot water flow in GPM. Secondary output estimates tankless BTU/hr at your rise using GPM × °F × 500.
This is a simultaneous-use planning tool—not a full fixture inventory or pipe-sizing calculator.
Concise answers for common searches — definitions, steps, and comparisons.
About 5.0 GPM from showers alone (2 × 2.5).
GPM × °F rise × 500.
Peak GPM is the sum of simultaneous fixture flow allowances. Tankless BTU/hr is estimated as peak GPM × temperature rise (°F) × 500.
Formula
peakGpm = showers×2.5 + sinks×1.5 + (dishwasher?1.5:0) + (washer?2:0); btu = round(peakGpm × tempRiseF × 500).Count fixtures that may run at the same time—not every fixture in the house.
Enable dishwasher and/or washer only when they contribute to the same peak moment.
Enter °F rise (about 30–100). Higher rise increases the tankless BTU estimate.
Use peak GPM as the flow target; use BTU/hr when comparing tankless capacity.
Input
ss 2 · sinks 1 · rise 70Output
6.5 GPM · ~227,500 BTU/hr2×2.5 + 1.5 = 6.5; 6.5×70×500 = 227,500.
Input
ss 1 · sinks 0 · rise 50Output
2.5 GPM · ~62,500 BTU/hr1×2.5 = 2.5; 2.5×50×500 = 62,500.
Common real-world scenarios where this tool saves time.
2 showers + 1 sink → 6.5 GPM; at 70°F rise ≈ 227,500 BTU/hr tankless class.
1 shower only → 2.5 GPM for a light simultaneous-use scenario.
Add washer running to raise peak GPM when laundry overlaps shower use.
Step-by-step chains that connect related tools for common tasks.
Estimate peak GPM here, then size tank or tankless equipment.
| Fixture | GPM allowance |
|---|---|
| Shower | 2.5 |
| Sink | 1.5 |
| Dishwasher | 1.5 |
| Washer | 2.0 |
Model morning peaks (showers overlapping) rather than theoretical maximums.
Compare the BTU/hr line to manufacturer GPM-at-rise charts before buying.
Enter only what can run together. Over-counting inflates GPM and BTU.
Colder inlet water needs a larger °F rise for the same outlet temperature.
This tool estimates flow demand. Use the Pipe Sizing Calculator for supply/drain diameters.
Advertisement
Showers × 2.5 GPM + sinks × 1.5 GPM, plus 1.5 GPM if the dishwasher is running and 2 GPM if the washer is running.
BTU/hr ≈ peak GPM × temperature rise (°F) × 500.
The difference between incoming cold water and the desired hot-water temperature, in degrees Fahrenheit.
No. Use the Water Heater Calculator’s tank mode for storage capacity from peak-hour gallons.
Yes. Low-flow fixtures deliver less. This calculator uses fixed planning allowances, not measured flows.
No. It is a planning estimate. Confirm equipment selection with manufacturer data and a licensed plumber.
Hot water flow inputs remain local — EverydayTools does not collect hot-water-flow calculator entries.
Estimates only — not professional plumbing advice. Verify with a licensed plumber and local code before installation.
Advertisement
Reviewed on 2026-06-28.
Same workflow or intent — pick the next step without leaving the site.
Weight-based daily hydration estimate with exercise and climate activity adjustments—results in liters, cups, and milliliters for drinking goals.
Free pipe volume calculator: inside diameter and length → US gallons, liters, cubic feet, water weight, and gallons per foot.
Free drain slope calculator: horizontal run and slope in/ft → total drop and percent grade with IPC minimum check. Runs locally in your browser.
Free water heater calculator: household size → tank gallon size or tankless GPM and BTU/hr. Tank and tankless modes. Runs locally in your browser.
Free pipe sizing calculator: fixture counts → WSFU and DFU totals with supply and drain pipe size recommendations. Runs locally in your browser.
Calculate how much PEX tubing you need in linear feet, add waste, and round up to full coils. Free PEX calculator for plumbing runs and material takeoffs.
Frequently opened tools from the same category.
Free adult BMI from height and weight (lb/ft/in or kg/cm). CDC category, healthy weight range, optional waist. Screening only—runs in your browser.
Estimate how many calories you need per day. Mifflin-St Jeor BMR, activity TDEE, and lose/gain starting points. US and metric. Runs in your browser.
Free tip calculator — find tip amount, bill + tip total, and per-person share. Presets for common percentages (10%, 15%, 20%), custom %, and equal split. Runs in your browser. No signup.
What is 20% of 500? Percent increase, decrease, difference, reverse %, markup & margin—runs locally in your browser, no upload. Copy results or share a link.
Cross-category tools others open in the same session.
What is 20% of 500? Percent increase, decrease, difference, reverse %, markup & margin—runs locally in your browser, no upload. Copy results or share a link.
Free JSON formatter — paste minified or messy JSON and instantly get beautified, indented output with syntax highlighting and error detection. Browser-based, no server upload. Runs locally in your browser when supported—no upload required for normal use.
Free word counter — live word, sentence, and paragraph counts plus reading time for essays, blogs, and SEO drafts. Runs locally in your browser.
Free adult BMI from height and weight (lb/ft/in or kg/cm). CDC category, healthy weight range, optional waist. Screening only—runs in your browser.
Guides and walkthroughs that reference this tool.
10 free browser calculators: BMI, tip, discount, overtime, GPA, compound interest. No upload—runs locally. No signup.
2026 roundup of BMI calculators—EverydayTools, CDC, NIH, Healthline, and Calculator.net compared on accuracy, privacy, units, and clinical context.
Browse full tool collections by topic.
Cold inlet to setpoint — used for tankless BTU estimate