Foot Pounds to Inch Pounds: Torque Wrench Ranges

Buying a Torque Wrench Without Losing a Factor of Twelve

Tool catalogues mix the two imperial torque scales without warning. One wrench is listed as 20–200, another as 25–250, and only the small print says which is inch-pounds and which is pound-feet. Get that wrong and you either buy a tool that cannot reach half your jobs, or you set it twelve times too high on a fastener that will not survive it.

1 ft·lbf = 12 in·lbf, exactly. A wrench topping out at 250 in·lbf reaches only 250 ÷ 12 = 20.83 ft·lbf — nowhere near a wheel nut, and no amount of pulling changes that.

Twelve Is Not an Approximation

Unlike almost every other conversion on a wrench, this one is exact by definition: a foot is twelve inches, the pound of force is identical, so the ratio is a clean integer. Any rounding you see comes from the source figure, never from the factor.

Two Wrenches, Not One

Because a single tool cannot cover an 8 in·lbf trim screw and a 140 ft·lbf hub nut, workshops keep a small inch-pound wrench beside a larger pound-foot one. Converting a spec tells you which of the two to reach for.

Capacity Is Not All Usable

The stated accuracy of a click wrench applies over its rated span, and the bottom fifth of the scale is generally outside it. A converted spec that lands at 8 % of capacity is a signal to fetch a smaller tool, not to dial it in anyway.

Checking a Spec Against Your Wrench's Span

Put the specification in as written

Enter the pound-foot figure and the inch-pound equivalent appears immediately. Because the factor is a whole number, small values stay tidy: 2.5 ft·lbf lands on exactly 30 in·lbf with nothing trailing.

See where it falls on the dial

Compare the converted number with the span engraved on your wrench. If it sits below a fifth of the maximum, the reading is outside the range the tool was certified over and the job wants a smaller wrench.

Flip the pair when a catalogue does

Product listings quote whichever scale flatters the tool. The swap arrows reverse the direction, and typing into either box works, so a page of mixed listings can be normalised to one scale before you compare prices.

Keep the figure for the calibration record

The per-field copy button gives you the number without any unit text, which is what a calibration log or a purchase note wants when the two scales are being recorded side by side.

Wrench Capacities by Drive Size, on Both Imperial Scales

Representative spans for the drive sizes most commonly stocked. Exact ranges vary by maker, but the pattern holds: the small drives live in inch-pounds and the large ones in pound-feet, with a deliberate overlap around 15–25 ft·lbf.

Drive	Typical span (ft·lbf)	Same span (in·lbf)	What it is for
1/4 in	1.67–16.67	20–200	Trim, electronics, bicycle and hobby fasteners
3/8 in, low range	5–75	60–900	Sump plugs, brake fittings, valve covers
3/8 in, standard	10–100	120–1,200	General engine bay work
1/2 in	25–250	300–3,000	Wheel nuts, suspension, driveline
3/4 in	100–600	1,200–7,200	Truck hubs, heavy plant, structural bolting

Calibration houses check a wrench at 20 %, 60 % and 100 % of its maximum. On the 1/2 in tool above that means 50, 150 and 250 ft·lbf — 600, 1,800 and 3,000 in·lbf — and it is a useful reminder of how much of the dial is genuinely covered by the certificate.

Whole Numbers Stay Whole

An integer factor means catalogue spans convert without a fog of decimals, so 5–75 becoming 60–900 is something you can check in your head.

Every Torque Unit in the Picker

Both searchable dropdowns list all thirteen units the app defines, which covers the metric wrench you may be comparing against on the same page.

Fast Enough for a Catalogue Page

Results land as each digit is typed, so working through a shortlist of candidate wrenches is a matter of seconds per model.

Choosing and Calibrating a Torque Wrench

What actually happens if I read an inch-pound spec as pound-feet?

You apply twelve times the intended load. A 90 in·lbf fitting set to 90 ft·lbf receives 1,080 in·lbf — the small bolt shears, the alloy thread strips, or the plastic housing splits. The tell is the wrench itself: if a spec needs a big 1/2 in bar for something you could hold in one hand, stop and convert before you pull.

How close to its setting is a click wrench supposed to be?

The widely used benchmark for setting-type and indicating-type wrenches is ±4 % of the value, with beam types allowed a little more and some precision ranges built tighter. Crucially that tolerance applies from about 20 % of capacity upward; below that the tool is simply out of its element, which is why the converted figure should be compared against the span and not just the maximum.

How often does a wrench need recalibrating?

The common industry guidance is whichever comes first of roughly twelve months or about five thousand cycles, tightened further if the tool is dropped, used near its limits, or covered by a quality system that demands more. A workshop clicking a wrench a few dozen times a day reaches the cycle count long before the calendar date.

Should I wind a click wrench down when I put it away?

Most makers ask for it to be returned to the lowest mark on the scale rather than all the way to zero, so the spring is relaxed without unseating the mechanism. Storing a tool parked at 250 ft·lbf keeps the spring compressed for months and is a slow way of drifting out of tolerance between calibrations.

Is a digital torque adapter a substitute for a second wrench?

Partly. An adapter that sits between a plain ratchet and the socket reads live and can usually display either imperial scale, which removes the mental conversion. It still has its own rated range and its own calibration interval, and it adds length to the tool, so it complements a dedicated small-range wrench rather than replacing one.