Foot pounds-force minute to BTU/second
ft·lbf/min
BTU/s
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 ft·lbf/min (Foot pounds-force minute) → 0.00002141779105766738 BTU/s (BTU/second) Just now |
Quick Reference Table (Foot pounds-force minute to BTU/second)
| Foot pounds-force minute (ft·lbf/min) | BTU/second (BTU/s) |
|---|---|
| 100 | 0.00214177910576673823 |
| 1,000 | 0.02141779105766738232 |
| 5,000 | 0.10708895528833691161 |
| 10,000 | 0.21417791057667382322 |
| 33,000 | 0.70678710490302361663 |
| 100,000 | 2.14177910576673823221 |
| 330,000 | 7.06787104903023616628 |
About Foot pounds-force minute (ft·lbf/min)
Foot pounds-force per minute (ft·lbf/min) equals approximately 0.02260 watts. It is used in US mechanical engineering for low-power applications and in the historical definition of horsepower: one horsepower was defined by James Watt as 33,000 ft·lbf/min — the rate at which a horse could lift coal from a mine. This unit is now mostly encountered in legacy engineering references and historical machinery specifications.
One mechanical horsepower = 33,000 ft·lbf/min. A hand-cranked generator might produce 2,000–5,000 ft·lbf/min of mechanical power output.
About BTU/second (BTU/s)
BTU per second (BTU/s) is a high-power thermal unit equal to approximately 1,055 watts. It is used in large-scale industrial heating, combustion engineering, and power plant heat rate analysis where BTU is the preferred energy unit and the timescale is seconds. One BTU/s is roughly the power of a small domestic gas boiler running continuously. The unit bridges the BTU-based thermal engineering tradition with second-based rate measurement.
A large industrial gas burner rated at 5 BTU/s delivers about 5,275 W of thermal power. A 1 BTU/s heat source could raise 1 lb of water by 1 °F every second.
Foot pounds-force minute – Frequently Asked Questions
Where does the number 3,960 come from in US pump sizing formulas?
The pump horsepower formula HP = (GPM × Head in ft) / 3,960 hides a chain of unit conversions. Water weighs 8.33 lb per US gallon. Multiplying GPM × Head × 8.33 gives ft·lbf/min. Dividing by 33,000 ft·lbf/min per hp gives horsepower. So 33,000 ÷ 8.33 ≈ 3,960. The number is so ubiquitous in US mechanical engineering that pump designers recognize it on sight, yet few remember the derivation. It breaks down for fluids other than water — multiply by specific gravity for anything denser or lighter.
What real-world tasks produce 33,000 ft·lbf/min?
Lifting 330 lbs (150 kg) at 100 feet per minute — roughly the speed of a slow freight elevator. Or lifting 33 lbs at 1,000 ft/min (a fast dumbwaiter). A human on a bicycle sustainably produces about 5,000–10,000 ft·lbf/min (0.15–0.3 hp). A small outboard boat motor produces about 165,000 ft·lbf/min (5 hp). The unit makes intuitive sense for lifting and hoisting — the original application Watt cared about.
Why use ft·lbf/min instead of ft·lbf/s?
Historical convention and practical timescale. Mine hoists, waterwheels, and early steam engines operated at rates naturally measured per minute — the machinery completed one cycle every few seconds to minutes. Watt himself measured horses per minute because that's how mine work was timed. The per-minute unit also gives larger, more manageable numbers: "33,000 ft·lbf/min" is easier to work with than "550 ft·lbf/s" when you're doing longhand arithmetic in 1780.
How much ft·lbf/min can a human sustain?
A healthy adult can sustain about 4,000–6,000 ft·lbf/min (roughly 90–135 W or 0.12–0.18 hp) of useful mechanical work for hours — think steady cycling or rowing. Short bursts reach 15,000–25,000 ft·lbf/min (0.5–0.75 hp). Elite cyclists sustain 12,000+ ft·lbf/min (0.4 hp) for an hour. By Watt's definition, a horse sustains 33,000 ft·lbf/min, meaning one horse ≈ 5–8 sustained humans. The ancient rule of "ten slaves per horse" wasn't far off.
Is 33,000 ft·lbf/min still used in any modern calculations?
Yes — it's embedded in US pump and fan engineering. The formula for pump horsepower is: HP = (GPM × Head in ft × Specific Gravity) / 3,960, where 3,960 = 33,000 / (8.33 lb/gal). The number 33,000 ft·lbf/min lurks inside every US pump sizing calculation, even if the engineer never writes it explicitly. It also appears in ASME standards for hoists, cranes, and elevators — anywhere lifting power needs to be specified.
BTU/second – Frequently Asked Questions
Why would anyone use BTU per second instead of kilowatts?
In US combustion engineering and power plant heat rate analysis, fuel energy content is natively specified in BTU (natural gas is sold per therm = 100,000 BTU). Expressing burner output in BTU/s keeps the calculation in one unit system, avoiding constant conversions. When your fuel flow is in BTU/min and your efficiency calculations use BTU, switching to watts mid-calculation just creates errors.
How does 1 BTU/s compare to everyday power levels?
One BTU/s ≈ 1,055 watts — roughly a single-bar electric fire or a small hair dryer. It's a surprisingly human-scale unit. A typical US home gas furnace running at full blast produces about 28 BTU/s (100,000 BTU/h ÷ 3,600). A gas stovetop burner on high delivers about 3–5 BTU/s. So BTU/s lands right in the range where you can feel the heat on your face.
What industries commonly use BTU per second?
Power plant thermal engineering (heat rate analysis), industrial furnace and kiln design, jet engine combustion analysis, and rocket propulsion engineering. NASA specifications for rocket engines often include BTU/s figures. The Space Shuttle Main Engine produced about 12 million BTU/s of thermal power. Steelmaking blast furnaces operate at 50,000–200,000 BTU/s of heat input.
How do you convert BTU/s to horsepower?
One BTU/s = 1.415 mechanical horsepower, or roughly 1.4 hp. This is useful in automotive and engine testing where dynamometers may report in BTU/s for thermal measurements but engineers think in horsepower. A 400 hp engine rejects about 280 BTU/s through its cooling system at full power (assuming 60% of fuel energy becomes waste heat). The conversion factor is easy to remember: multiply BTU/s by 1.4 to get hp.
What is a BTU anyway and why does America still use it?
A BTU (British Thermal Unit) is the energy needed to raise 1 pound of water by 1°F — about 1,055 joules. Despite the name, Britain abandoned it decades ago. America keeps it because the entire HVAC, natural gas, and building industry infrastructure — codes, equipment ratings, contractor training — is built around BTU. Switching would require rewriting thousands of standards and retraining millions of technicians. It's inertia, pure and simple.