Torque Calculator

How to use this calculator

Pick the mode. Tap "Bolt Torque" if you're tightening a generic fastener (cylinder head, suspension link, axle bolt). Tap "Lug Nut Torque" if you're putting wheels back on.
Bolt mode: pick metric or imperial, the bolt size, the grade or class (Class 8.8 / 10.9 for metric, Grade 5 / 8 for imperial), and the lubrication or finish. Lubrication slashes the required torque by up to 50% — anti-seize on a "dry" spec is a great way to snap the bolt.
Lug mode: pick the stud size (look at the actual stud, not the lug nut — the stud has a thread pitch like 12mm × 1.5 or 1/2" × 20). The vehicle hint on each chip tells you which class of car typically uses that stud.
Read the result. Three numbers update live — ft-lb, Nm, in-lb. The colored chip tells you the wrench class you need (1/4", 3/8", 1/2", or 3/4" drive). Plain-English summary explains the spec in mechanic terms.
Save it. Hit "Share" to copy a link with the exact bolt or stud preserved (text it to a friend, drop in a forum thread). Hit "PDF" for a one-page torque card you can keep in the toolbox.

Why this calculator is different from other torque calculators

Most torque calculators on the first page of search results are either dry industrial sensor-brand calcs (Futek, Engineers Edge), unit-conversion utilities (Mountz), or generic physics calcs that confuse engine torque with bolt-tightening torque. None of them know you're standing in a driveway with a click-style wrench in one hand and a service manual you can't quite read in the other. Here's what we did differently:

Two modes in one URL — bolt + lug nut. Most search results force you to a separate page for lug nut specs (usually behind Discount Tire's vehicle-lookup wall). We pair the engineering formula calc with the wheel-stud chart. Same URL, same share link, both intents handled.
Mechanic-flavored, not industrial. Mike Reeves (ASE Master Tech) signs the math. Plain-English summary tells you which drive size you need ("3/8" drive, 15–80 ft-lb range — covers most engine accessories") instead of just spitting a number. The K-factor selector reads "Anti-seize / heavy lube" not "K = 0.10 dimensionless coefficient."
Live tri-unit display. Every result shows ft-lb, Nm, and in-lb at once, with tabular figures so the digits don't jitter as you change inputs. Got a 3/8" drive Nm-only torque wrench? The Nm number is right there. Got an in-lb wrench for a small bolt? The conversion is built in. Top SERP entries make you switch tabs or go to a separate converter.
Embeddable widget. None of the top 10 organic results offer an embed snippet. This means trailer build threads, motorcycle forum sticky posts, YouTube wrench-channel show-notes pages, and shop blogs can drop the calculator directly into their content with one line of HTML — same math, persona attribution intact.
K-factor table is on the page. The reason a lubricated bolt needs less torque than a dry bolt is friction in the threads — that's what K represents. We expose K right next to each lubrication option (K=0.20 for dry plain steel, K=0.10 for anti-seize) so you can see why an oily bolt at the dry torque spec is going to snap.
Star pattern + two-pass tightening reminder appears on every lug-nut result, with a re-torque-after-50-miles note for aluminum wheels. Most lug-nut SERP entries show a number and stop there.
Branded printable torque card. One-page PDF with the bolt or stud, the spec in three units, the wrench class, and the star-pattern reminder — keep it in the toolbox or hand it to whoever's borrowing your wrench.

How this calculator works (the math)

Bolt torque is mostly about friction, not the bolt itself. About 85–90% of the torque you apply with a wrench fights friction in the threads and under the bolt head; only the remaining 10–15% actually becomes useful clamping force. That's why the canonical formula isn't just "T equals force times distance."

The T = K × D × F formula

Used by every authoritative engineering reference (Engineering Toolbox, Omni Calculator, Futek, Portland Bolt, Fastenal):

T = K × D × F × (1 − L/100)

T — applied torque (Nm or lb-ft)
K — nut-factor / friction coefficient (dimensionless; depends on bolt finish + lubrication)
D — nominal bolt diameter (m or ft)
F — desired axial clamp force / preload (N or lbf)
L — additional lubrication factor (% reduction; usually 0 if K already accounts for the finish)

K-factor (the friction coefficient)

K is what the surface finish and any lubrication contribute to thread friction. Ballpark values used across every credible source (Crest Fasteners, Engineering Toolbox, Futek, Fastenal):

Dry plain steel — K = 0.20 (the default on most charts)
Zinc-plated — K = 0.20 (same as dry plain — the zinc doesn't reduce friction much)
Black-oxide / phosphate — K = 0.30 (rougher; increases required torque)
Lightly oiled — K = 0.18
Cadmium-plated — K = 0.16
Anti-seize / heavy lube — K = 0.10 (cuts torque almost in half)
Moly (MoS₂) — K = 0.13 (ARP-style assembly lube)

If a service manual says "180 ft-lb dry" and you put anti-seize on the threads, you're now applying roughly twice the clamping force you should be — which is how aluminum heads crack and threads strip. Match the K to what's on the bolt.

F (clamp force) defaults to 75% of proof load

Industry convention is to torque a bolt to 75% of its minimum proof load. Proof load is the biggest pull the bolt can take before any permanent stretch. We use 75% to leave a safety margin — enough preload to hold the joint, not so much that the bolt yields.

Proof stress (ISO 898-1 for metric, SAE J429 for imperial), times the bolt's tensile-stress area, gives proof load. Multiply by 0.75 — that's our default F.

Why the result is approximate (the ±25% problem)

Per Fastenal's own disclaimer (and SAE engineering convention), even a perfect input torque gives a variation of preload by as much as 25%. That's because real K-factors drift with rust, dirt, hole misalignment, thread damage, and torque-wrench calibration. The number this calculator gives you is the right starting point — but it's not a substitute for an OEM-specific spec when you have one. Always verify in the owner's manual or service data for the actual joint.

Sources used

Common bolt-torque values

M10 × 1.5 Class 8.8 dry — 37 ft-lb / 50 Nm

The everyday automotive bolt — engine accessory brackets, intake manifolds, suspension link bolts on compact and mid-size cars. Use a 3/8" drive click wrench in the 15–80 ft-lb range. If a service manual lists this as 35–40 ft-lb, that's the same number — manufacturer ranges absorb K-factor variance.

M12 × 1.75 Class 8.8 dry — 65 ft-lb / 88 Nm

Bigger suspension and chassis bolts on most passenger cars. Still a 3/8" drive job, but you'll want a wrench that goes to at least 80 ft-lb. Lubricate this bolt with anti-seize and the right torque drops to ~32 ft-lb — half-spec.

1/2" × 13 Grade 8 dry — 106 ft-lb / 144 Nm

Domestic trucks, hot rods, and older muscle cars. This is wheel-and-suspension territory — a 1/2" drive torque wrench is the right tool. A 3/8" drive will technically do it but at the upper limit of its accuracy band.

5/8" × 18 Grade 8 dry — 212 ft-lb / 287 Nm

Heavy trucks, trailers, and big aftermarket suspension hardware. A 1/2" drive long-handle (or 3/4" drive) is the right wrench. Don't try to hit 200+ ft-lb with a stubby 3/8" drive — you'll either under-torque, snap the wrench, or both.

Lug nut torque chart by stud size

These ranges are aggregated from Speedway Motors, RaceCar Engineering, Vivid Racing, and current OEM service data for the listed vehicle classes. The number on your owner's manual or door-jamb-area sticker overrides anything below — but if you've lost the manual, this is the right starting range:

10mm × 1.25 / 1.5 — 50–60 ft-lb (68–81 Nm) — subcompact, ATV, motorcycle, small trailer
12mm × 1.25 — 70–80 ft-lb (95–108 Nm) — compact (Honda Civic, Mazda3, Subaru Impreza)
12mm × 1.5 — 75–85 ft-lb (102–115 Nm) — older compact/mid-size (Toyota, Honda)
14mm × 1.5 — 80–95 ft-lb (108–129 Nm) — mid-size sedan, crossover, light SUV (Camry, RAV4, CR-V, MDX)
14mm × 2.0 — 90–110 ft-lb (122–149 Nm) — heavier SUV, German performance
7/16" × 20 — 70–80 ft-lb (95–108 Nm) — older imports, custom hot-rod, small trailers
1/2" × 20 — 85–100 ft-lb (115–135 Nm) — domestic compact / mid-size, light truck (older Mustang, GM A-body)
9/16" × 18 — 110–130 ft-lb (149–176 Nm) — heavy truck (F-150, Silverado 1500), full-size SUV
5/8" × 18 — 130–160 ft-lb (176–217 Nm) — heavy-duty pickup (F-250 / 350, Silverado HD), heavy trailer

How to find your stud size: open the door, look at the wheel. The threaded post sticking out of the hub is the stud. The first number is the diameter (10mm, 12mm, 1/2"), and the second is the thread pitch — for metric, threads-per-mm-of-pitch (1.5 means a thread every 1.5mm). Most autoparts counters can read it off in two seconds with a thread gauge.

Star pattern, two passes — why and how

Lug nuts get torqued in a star pattern, never around-the-clock, and always in two passes. Here's why and exactly how:

Snug all lugs by hand in a star (cross) sequence — opposite to opposite. If the wheel has 4 lugs, that's 12 → 6 → 3 → 9 (clock positions). For 5 lugs, draw a star — top, bottom-right, top-left, bottom-left, top-right. For 6 lugs, opposite-pair around the circle.
Tighten to half-spec on the first pass — same star sequence. If the spec is 90 ft-lb, the first pass is ~45 ft-lb. This pulls the wheel down evenly against the hub.
Tighten to full spec on the second pass — same sequence. Now you're at the recommended number. Do not "go around again" — that just over-torques.
Re-torque after the first 25–50 miles, especially on aluminum / mag wheels. Aluminum relaxes a small amount under the nut; the second torque check catches that.

Why a star pattern: a wheel hub face is precisely flat, but if you torque one lug full-spec and then the lug across from it, the wheel can sit slightly cocked. The star sequence pulls the wheel into the hub evenly. The two-pass rule does the same thing — by setting half-spec first, you let the wheel settle before you commit to full spec.

Frequently asked questions

How do I calculate torque on a bolt?

The industry formula is T = K × D × F: the torque you apply equals a friction coefficient K (typically 0.20 for dry plain steel) times the nominal diameter D times the desired clamp force F. F is normally set to 75% of the bolt's minimum proof load — that's the safety-margin convention used by Engineering Toolbox, Omni Calculator, and Fastenal. This calculator does that math for you when you pick a size + grade + lubrication.

How much is 250 Nm of torque?

250 Nm equals 184.39 ft-lb (or about 184 ft-lb in everyday rounding). That's heavy truck / heavy-duty suspension territory — bigger than passenger-car lug nuts. Use a 1/2" drive long-handle or 3/4" drive torque wrench. Toggle to either unit on this tool to see the conversion live.

Is 80 ft-lb enough for lug nuts?

Depends on the stud size. 80 ft-lb is on-spec for 12mm × 1.5 (compact / mid-size) and at the low end for 14mm × 1.5 (mid-size SUV). For 1/2" × 20 or 9/16" × 18 studs (light trucks, full-size SUVs), 80 ft-lb is undertorqued — the nut may loosen on the road. Always match the stud spec, not a single number you remember.

What is the 90/10 rule of torque?

The "90/10 rule" refers to how torque on a bolt is consumed: roughly 90% goes to overcoming friction in the threads and under the bolt head, and only the remaining ~10% actually becomes clamping force. That's why lubrication has such a huge effect on the right torque value, and why torque wrenches are only ±25% accurate at preload — most of what you're measuring is friction, not clamp.

Is engine torque measured in ft-lb or lb-ft?

Both terms appear in the field, but SAE convention says lb-ft is the official unit for engine torque (and ft-lb is the equivalent unit for tightening torque). Practically, the two are the same number — they just describe the geometry differently. This tool displays ft-lb because it's the consumer-friendly convention and the one printed on most retail torque wrenches.

Ft-Lbs to Nm Torque Converter — when you already have the spec and just need to flip units. Three linked fields (ft-lb / Nm / in-lb) with mechanic-flavored quick-fill chips for spark plugs, oil drain plugs, and lug nuts.
Bar to PSI Converter — for the tire pressure side of the wheel job. Most US gauges read PSI; most Euro and Japanese owner's manuals spec bar or kPa. Convert live.
Wheel Offset Calculator + Visualizer — when you're swapping wheels, the new offset changes how the wheel sits in the fender. See poke and tuck before you buy.
Browse all free tools by Mike Reeves →

Mike's recommendations for actually applying these numbers

A torque calculator only matters if you have a wrench that can hit the number. Three categories cover almost every torque job on a passenger vehicle:

Best Torque Wrenches — a click-style 1/2" drive (30–250 ft-lb) covers lug nuts, suspension, brake calipers, and most engine bolts on a passenger car. Add a 3/8" drive (15–80 ft-lb) for engine accessories and small fasteners. A digital wrench is the gold standard if you do this often. Don't trust an impact gun for a final torque pass — they're for breaking loose and snugging, never for spec.
Best Mechanic Tool Sets — a 3/8" drive set with deep sockets in metric and SAE is the daily-driver of bolt work. The torque wrench rides on a ratchet handle, not the wrench's own. Most homeowners are best served by a mid-tier 200-piece set rather than three small specialty boxes.
Best Impact Wrenches — to break loose stuck lug nuts (rusty studs, over-torqued by the tire shop's air gun) and snug them back up to ~30 ft-lb before final torquing. Cordless 1/2" impacts in the 600+ ft-lb range cover almost any passenger-car job. Always do the final torque pass with a click-style torque wrench, never the impact.

Sources & methodology

The Engineering ToolBox — Bolt Torque Calculator — canonical T = KDF formula, K-factor table, ±25% accuracy convention.
Omni Calculator — Bolt Torque Calculator — formula validation, lubrication-factor model.
Fastenal — Torque Calculator — engineering disclaimer + ±25% wrench-accuracy industry convention.
Crest Fasteners — What is Proper Torque (PDF) — K-factor table + 75%-of-proof-load convention.
Portland Bolt — Bolt Torque Chart — verification of imperial torque values.
Speedway Motors — Wheel Lug Nut Torque Spec Chart — primary lug-nut chart source.
RaceCar Engineering — Tec-Lug Nut Torque Specs — secondary lug-nut chart.
ISO 898-1 (metric proof stresses) and SAE J429 (imperial proof stresses) — bolt grade standards.

The 22 fixture cases this tool is tested against are in fixtures.json alongside the component source. About Mike Reeves · Last reviewed April 28, 2026.

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  Bolt &amp; lug-nut torque calculator by
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  &middot; Reviewed by Mike Reeves, ASE Master Technician
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Bolt and Lug Nut Torque Calculator