Water Heater Size Calculator
Find the right tank size and first hour rating for your household
Enter the number of times each activity occurs during your busiest morning hour.
| Tank Size (gal) | Typical FHR (gal/hr) | Recovery Rate | Fuel Type | Best For |
|---|---|---|---|---|
| 30 | 40–52 | ~21 GPH (elec) / ~33 GPH (gas) | Electric / Gas | 1–2 people |
| 40 | 52–60 | ~21 GPH (elec) / ~35 GPH (gas) | Electric / Gas | 2–3 people |
| 50 | 58–70 | ~22 GPH (elec) / ~40 GPH (gas) | Electric / Gas | 3–4 people |
| 60 | 65–80 | ~23 GPH (elec) / ~43 GPH (gas) | Electric | 4–5 people |
| 75 | 75–100 | ~25 GPH (elec) / ~55 GPH (gas) | Electric / Gas | 5–6 people |
| 80 | 80–110 | ~26 GPH (elec) / ~60 GPH (gas) | Electric | 6+ people |
| Activity | Hot Water Used | Duration | Notes |
|---|---|---|---|
| Shower (8 min) | 10 gal | 8 min | ~1.25 GPM hot water avg |
| Bath (full tub) | 20 gal | 10–15 min fill | Varies by tub size |
| Shaving | 2 gal | ~5 min | Running water at sink |
| Hand Washing | 1 gal | ~2 min | Per wash cycle |
| Dishwasher (cycle) | 6 gal | ~1 hr cycle | Draws hot at start |
| Clothes Washer (hot) | 7 gal | Per load | Full hot wash cycle |
| Clothes Washer (warm) | 4 gal | Per load | Warm wash cycle |
When you choose a water heater, the right size is very important for comfort and saving money. If the device is too small, it will not meet the needs for hot water. On the other hand, too big a model wastes energy and money The capacity of tanks is measured in gallons, and most commonly you choose models of 30, 40, 50 or 75 gallons.
To find the right size of tank for home, including heat pump water heaters, the “first hour rating” is a useful number. This rating shows how many gallons of hot water the water heater can give during one hour, starting when the tank is fully full.
How to Choose the Right Size Water Heater
General rule is have around 15 gallons for every family member. So, family of two people will need about 30 gallons, while family of four people will need at least 50 to 60 gallons. For an average family of four, a 40-gallon water heater usually sufficess.
Family of four could use 50-gallon electric water heater, or 40 gallons if it is gas. Counting the size by number of bedrooms is not the best way, because a three-bedroom house can have only two folks or even five. More important is how many folks live here, how long they shower and whether they bathe one after the another.
For standard family, you want at least 40 or 50 gallons. Smaller models are rare. For instance, mobile home could have 30-gallon water heater, but that does not always work for filling a standard tub.
The figures in general guidelines are only marks and maybe do not exactly match your needs. Family of five people may live comfortably with 30-gallon tank, while family of two may find it too small. Even so, for two people with one bathroom and washer, 30 gallons usually work.
For every extra bathroom, you should add about three and a half gallons to the capacity.
50- or 65-gallon water heater could work for couples in houses with two floors, depending on how they use the water. If in big family all want to bathe in the morning, maybe a tank of 50 or even 65 gallons is needed. You can also look at the water bills of the summer for help the choice, because then you take a lot of baths and showers.
Other option is use tankless water heater. When you choose such model, the size of the old water heater does not matter. Here it is only about the flow of the water and the wanted temperature.
Family of four usually needs tankless model, that gives eight to ten gallons each minute. Also the time, how the water needs for warm, is a thing thatyou must consider.
