What Is Cost Per Therm?
Cost per therm tells you how much you pay for each therm of natural gas energy. Since one therm equals 1,000 cubic feet of natural gas, this metric translates the raw volume on your utility bill into a meaningful cost-per-energy figure. Whether you are budgeting for winter heating or evaluating a new gas supplier, knowing your cost per therm gives you a clear number to compare against.
Natural gas is one of the most widely used energy sources for residential heating, cooking, and water heating. By tracking your cost per therm over time, you can spot seasonal rate changes, detect unusual consumption spikes, and decide whether switching energy sources would save you money.
How to Calculate Cost Per Therm
The formula converts gas volume into therms and then divides by total cost:
[\text{Cost Per Therm} = \frac{\text{Total Cost}}{\text{Volume (ft}^3\text{)} \div 1{,}000}]
Where:
- Total Cost ($) is the amount you paid for your gas.
- Volume (ft³) is the total volume of gas consumed in cubic feet.
- 1,000 is the number of cubic feet in one therm.
If your bill reports volume in cubic meters instead of cubic feet, convert first using the factor 1 m³ = 28.3168 ft³:
[\text{Volume (ft}^3\text{)} = \text{Volume (m}^3\text{)} \times 28.3168]
Calculation Example
Scenario: Your monthly gas bill is $1,500 and you consumed 2,500 ft³ of natural gas.
First, convert volume to therms:
[\text{Therms} = \frac{2{,}500}{1{,}000} = 2.5]
Now calculate cost per therm:
[\text{Cost Per Therm} = \frac{1{,}500}{2.5} = 600]
Your cost per therm is $600/therm.
Metric Example
If your bill shows 70 m³ at a total cost of $420:
Convert cubic meters to cubic feet:
[70 \times 28.3168 = 1{,}982.18 \text{ ft}^3]
Convert to therms:
[\frac{1{,}982.18}{1{,}000} = 1.982]
Calculate cost per therm:
[\frac{420}{1.982} \approx 211.90]
Your cost per therm is approximately $211.90/therm.
Comparing Gas Costs Across Seasons
Tracking cost per therm across billing periods reveals how rates and consumption shift throughout the year:
| Month | Total Cost ($) | Volume (ft³) | Therms | Cost Per Therm |
|---|---|---|---|---|
| January | 280 | 3,200 | 3.2 | $87.50 |
| April | 95 | 1,100 | 1.1 | $86.36 |
| July | 40 | 400 | 0.4 | $100.00 |
| October | 120 | 1,500 | 1.5 | $80.00 |
Summer months often show a higher cost per therm because fixed service charges are spread over a smaller volume of gas. You can use this insight alongside your cost per kWh to decide whether gas or electricity is more economical for specific appliances.
Tips for Managing Gas Costs
- Compare suppliers. In deregulated markets, multiple gas suppliers compete on the per-therm rate. Shopping around annually can yield meaningful savings.
- Upgrade equipment. High-efficiency furnaces (95%+ AFUE) extract more usable heat from each therm, lowering your overall energy cost relative to older equipment.
- Insulate and seal. Air leaks and poor insulation force your heating system to burn more gas. Weatherstripping, caulking, and attic insulation pay for themselves quickly.
- Use a programmable thermostat. Reducing temperature by a few degrees during sleep and when the house is empty can cut annual gas consumption by 10% or more.
Related Calculators
- Cost Per kWh Calculator
- Cost Per BTU Calculator
- Cost Per Gallon Calculator
- Cost Per Day Calculator
- Cost Per Unit Calculator
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