Water heater sizing Last reviewed June 30, 2026
40 vs 50 Gallon Water Heater: Which Size Do You Need?
By the WhatSize editorial team 4 min read Standards-reviewed
Choose a 40-gallon water heater for 1-3 people who stagger their hot-water use, especially with a fast-recovering gas unit. Choose a 50-gallon for 3-4 people, simultaneous showers, or an electric heater, which recovers more slowly and benefits from the extra reserve.
The Gap Is About Peak Demand and Recovery
The difference between 40 and 50 gallons is not just ten gallons of storage, it is how much buffer you have during the busy morning hour. The DOE First Hour Rating (FHR) combines the tank volume with how fast the unit reheats, so a fast-recovering gas heater can deliver more hot water than its tank size suggests, while a slower electric heater delivers less.
That is why a 40-gallon gas heater often keeps up with the same household as a 50-gallon electric. If your demand is modest and recovery is fast, 40 gallons saves money and space. If showers overlap or recovery is slow, the 50-gallon reserve prevents cold surprises.
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.
Decision Guide: 40 vs 50 Gallon
- Choose 40 gallon if: 1-3 people, showers are staggered, gas heater with fast recovery, or you need to fit a tight space
- Choose 50 gallon if: 3-4 people, showers often overlap, or an electric heater with slower recovery
- Choose 50 gallon if: you have a large soaking tub or expect demand to grow
- Either way: compare the First Hour Rating, not just the gallon number, when choosing between two models
Frequently asked questions
Should I get a 40 or 50 gallon water heater?
Pick 40 gallons for one to three people with staggered use, particularly a gas unit that recovers quickly. Pick 50 gallons for three to four people, frequent simultaneous showers, or an electric unit, since the larger reserve covers the slower recovery.
Is a 50-gallon water heater worth the extra cost?
If your household runs hot water at overlapping times, yes, because running out mid-shower is the most common sizing complaint. If your demand is light and staggered, a 40-gallon unit costs less to buy and heat without leaving you short.
Does a 40-gallon gas heater equal a 50-gallon electric?
Often, yes, in practice. Gas heaters recover much faster, so a 40-gallon gas unit can have a similar or higher First Hour Rating than a 50-gallon electric. Compare the FHR of the specific models rather than the tank size alone.
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
- Tankless Water Heater GPM Chart by Household Size
- Water Heater UEF Rating Explained: Energy Factor vs FHR Chart
- What Size Water Heater for a 2-Bathroom House?
Still choosing between sizes? Compare: tank vs tankless