Propane tank days-left calculator

Read the gauge (or weigh a cylinder), list what burns propane, and see how many days you have left.

52days of propane

Runs out about —

300 gal (1,260 lb) left · 5.69 gal a day

Reorder at 20% in 35 days

What you have
%
%
How fast you use it

520,000 BTU a day ÷ 91,452 BTU per gallon

  • Free
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  • Works offline
  • Data stays on this device
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How it's calculated

  1. Bulk tank: gallons left = tank size × gauge reading %. Tanks are only filled to about 80% of capacity, so a full tank shows about 80% (Propane Education & Research Council).
  2. Cylinder: pounds of propane = weight on a scale − tare weight stamped on the collar (TW). Gallons = pounds ÷ 4.2 lb per gallon (PERC). A 20 lb grill cylinder holds about 4.7 gallons and weighs about 18 lb empty.
  3. Daily use from appliances = each appliance's BTU per hour (from its rating plate) × hours it runs per day, added up, ÷ 91,452 BTU per gallon (US Energy Information Administration).
  4. Days left = gallons left ÷ gallons per day. The refill line shows the days until the gauge reaches the percentage you want to reorder at.
  5. Appliances rarely run at full rating all day, so hours per day is the number to adjust: a furnace that runs 15 minutes in every hour runs 6 hours a day.

Worked example

A 500-gallon tank reads 60%, so it holds 500 × 0.60 = 300 gallons. An 80,000 BTU/h furnace running 6 hours a day and a 40,000 BTU/h water heater running 1 hour use 520,000 BTU a day ÷ 91,452 = 5.69 gallons a day. 300 ÷ 5.69 = 52.8, so 52 days. Reordering at 20% leaves 200 gallons to burn first: 35 days.

Sources

Questions

Why does my full tank read 80%, not 100%?

Propane expands when it warms, so tanks are filled to about 80% to leave room. 80% on the gauge is a full tank.

How do I check a grill cylinder without a gauge?

Weigh it on a bathroom scale and subtract the tare weight stamped on the collar (marked TW). Switch the calculator to "Weigh a cylinder".

Where do I find an appliance's BTU rating?

On its rating plate or in the manual, usually as "input BTU/hr". The calculator multiplies it by the hours you expect it to run each day.

Does it work for LPG cylinders in kilograms?

Not directly yet: it works in US gallons and pounds. The full GasBook app is built around kg cylinders and learns your burn rate from refills.

By the All Things AI team · Last tested · Questions or a wrong number? support@allthingsn.com

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