Water heater sizing Last reviewed June 2026
Tankless Water Heater GPM Chart by Household Size
By the WhatSize editorial team 4 min read Standards-reviewed
A whole-house tankless water heater typically delivers 6-10 GPM at a 60-70°F temperature rise. A 2-bathroom home with 3-4 occupants needs 6-7 GPM. A 3-bathroom home with 5+ occupants needs 8-10 GPM. Sizing is determined by counting fixtures that may run simultaneously, not by household size alone.
How tankless GPM is measured
Unlike tank water heaters (sized by FHR), tankless water heaters are sized by GPM (gallons per minute) — how much hot water they can deliver on demand, at a given temperature rise. A tankless rated for 9 GPM at a 35°F rise may only deliver 6 GPM at a 65°F rise (the typical cold-to-hot temperature difference in northern US homes).
The temperature rise is critical: if your groundwater is 50°F and you want 120°F output, you need a 70°F rise. The same heater will deliver more GPM in Florida (groundwater 70°F, 50°F rise) than in Maine (groundwater 45°F, 75°F rise).
Manufacturer spec sheets always list GPM at multiple temperature rises. Use the rise that matches your climate.
Top picks for this size
These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.
GPM chart by household and simultaneous fixtures
Tankless GPM sizing by household
| Household | Typical GPM needed (60°F rise) | Tankless unit |
|---|---|---|
| 1-2 people, 1 bath | 3-5 GPM | Small point-of-use or 6 GPM whole-house |
| 3-4 people, 2 baths | 5-7 GPM | 7-8 GPM whole-house |
| 5-6 people, 3 baths | 7-9 GPM | 8-10 GPM whole-house (or two units) |
| 7+ people, 4+ baths | 9-12 GPM | Commercial-grade or two parallel units |
How to count simultaneous fixtures
Typical fixture GPM draw (with aerator):
- Shower (standard): 2.0-2.5 GPM
- Shower (low-flow): 1.5 GPM
- Kitchen faucet: 1.5-2.0 GPM
- Bathroom faucet: 0.5-1.0 GPM
- Dishwasher: 1.0-1.5 GPM
- Washing machine: 2.0-3.0 GPM (rarely runs while showering)
Add up the GPM of all fixtures that could run at the same time during your peak usage (typically: morning shower + kitchen cleanup + someone brushing teeth). That sum is your target tankless GPM, with 1-2 GPM margin.
For more on tank vs tankless tradeoffs, see our tank vs tankless comparison. Use our free water heater calculator for your specific household.
Frequently asked questions
What GPM tankless do I need for a family of 4?
A family of 4 with 2 bathrooms typically needs 6-8 GPM at a 60°F temperature rise. A 7-8 GPM whole-house tankless handles this with margin. If you live in a cold climate (groundwater below 50°F), size up to 9-10 GPM to account for the higher temperature rise.
Is 6 GPM enough for a house?
6 GPM is enough for a 1-2 bathroom, 1-3 person household. It supports one shower (2.0 GPM) plus a faucet (1.0 GPM) plus a dishwasher (1.5 GPM) = 4.5 GPM with 1.5 GPM margin. For 3+ bathrooms or 4+ people, go to 8+ GPM.
How many GPM is a typical shower?
A standard US shower head uses 2.0-2.5 GPM. Low-flow shower heads (mandatory in some states) use 1.5-1.8 GPM. Older shower heads (pre-1992) can use 3.5-5 GPM. If you're sizing a tankless, count your shower's actual GPM.
You might also need
More water heater sizing guides
- What Size Water Heater for a 1-2 Person Household?
- What Size Water Heater for a 3-4 Person Household?
- What Size Water Heater for a Family of 5?
- Tank vs Tankless Water Heater: Which Size Is Right?
- What Size Water Heater for Electric vs Gas Homes?
- Water Heater FHR Chart: First Hour Rating by Household Size
- Water Heater UEF Rating Explained: Energy Factor vs FHR Chart