Spur Gear Set Designer
Design your gear set based on many factors such as your application for aerospace, heavy industry and more. Give the sheet what you know about the job and it returns a complete, checked pinion and gear you can refine and compare.
Updated: 7/9/2026
Start with your job
Power to transmit
hp
Input speed
rpm
Ratio
: 1
How much the set slows the output. A value under 1 speeds it up instead.
Rated: OK
C 8.250 in · F 4.13 in · 33:99 T · ~430 lb
That is all the sheet needs. It fills in the rest from the industry you pick below. Want the controls? Open
Fine-tune the design
to set loading, pressure angle, proportions, finishing and oil yourself.
The pair as it would run - drag to orbit. 33-tooth pinion (blue) and 99-tooth gear at C = 8.250 in, gear phased so its teeth enter the pinion’s spaces on the line of centers.
Pick your industry
each follows a recognized industry standard
Lightest
60/60 HRC carburized
C 5.20 in · ~48 lb
Normal / medium
335/300 HB through-hardened
C 8.25 in · ~430 lb
Oil & Gas (API 613)
Carburized HRC 59
C 7.33 in · ~302 lb
Aerospace
60/60 HRC carburized
C 5.20 in · ~48 lb
Basic industrial
335/300 HB through-hardened
C 8.25 in · ~430 lb
Automotive
59/59 HRC carburized
C 5.75 in · ~58 lb
Turbine drive
335/300 HB through-hardened
C 9.56 in · ~667 lb
Every card is the same job, sized the way that industry expects, with its center distance,
weight and a look at the pair. The tougher the standard, the smaller and lighter the set, paid for with harder steel, tighter
tolerances and, in a few cases, a shorter rated life.
Industry
Hardness
Prime mover
Driven equipment
Using the preset’s default Ka = 1.00 - pick a driven equipment class to look it up from Table 5.37.
Pressure angle
Aspect ratio F/d₁ = 1.00
Finishing
Oil
Blank temperature
°F
Force pinion teeth (advanced)
Force diametral pitch (advanced)
Every field here is optional. The sheet already has a full answer without them.
The pair, side by side
| Center distance C | 8.2500 in |
| Face width F F/d₁ = 1.00 | 4.125 in |
| Diametral pitch Pd Table 3.12 standard | 8 1/in (m 3.18 mm) |
| Teeth z₁ : z₂ | 33 : 99 |
| Ratio (actual) | 3.0000 : 1 |
| Speeds | 1,800 rpm pinion · 600.0 rpm gear |
| Input torque Eq 4.62 | 3,501 in·lb |
| Tangential load Wt Eq 4.64 | 1,698 lb |
| Pitch-line velocity | 1,944 fpm |
| Contact ratio mp AGMA floor 1.2 | 1.69 |
| Design backlash Table 3.4 | 0.008 in |
| Estimated weight Eq 4.60 | ~430 lb |
Pinion · the fast member, 33 T
| Teeth | 33 (Table 3.7 band 19–38) |
| Speed | 1,800 rpm |
| Pitch diameter d | 4.1250 in |
| Outside diameter | 4.4775 in |
| Root diameter | 3.9150 in |
| Addendum coef 1.410 (x = +0.410) | 0.1763 in |
| Whole depth Table 3.13 | 0.2813 in |
| Max tooth thickness theoretical − B/2 | 0.2297 in |
Gear · the slow member, 99 T
| Teeth | 99 |
| Speed | 600.0 rpm |
| Pitch diameter d | 12.3750 in |
| Outside diameter | 12.5225 in |
| Root diameter | 11.9600 in |
| Addendum coef 0.590 (x = -0.410) | 0.0738 in |
| Whole depth Table 3.13 | 0.2813 in |
| Max tooth thickness theoretical − B/2 | 0.1550 in |
How hard the set is working
K-factor (surface durability, Eq 4.68)133 / 180 psi · 1.35× margin
allowable index 180 psi ÷ Ka 1.00 = design 180.0 psi
Unit load (bending strength, Eq 4.66)3,292 / 4,500 psi · 1.37× margin
allowable 4,500 psi ÷ Ka 1.00 = design 4,500 psi
Scoring criterion Zc (Eq 4.50)2,305 / 12,000 · 5.21× margin
AGMA 7 (heavy) at 150 °F blank (Table 4.11)
OKKa 1.0010⁸ cyclesMedium precision335/300 HB through-hardened
Tooth stress, up close
Bending st - pinion (Eq 5.90)33,912 / 46,350 psi · 1.37× margin
Kt 3.42 (Table 5.34, tip-loaded) · 10⁸ cycles
Bending st - gear34,843 / 47,623 psi · 1.37× margin
Kt 3.51 · 3.3×10⁷ cycles (gear turns 1/mG as often)
Contact sc (Eq 5.95)112,477 / 130,837 psi · 1.16× margin
Ck 5,620 (Eq 5.114, Cp 2300; I = 0.1256 at the pinion LPSTC, Fig 5.36 basis)
Ka 1.00Km 1.60Ks 1.00Kv 0.53Kd = 3.01allowables: index-derived from the Table 4.16 practice (allowable-stress charts Figs 5.24–5.27 are not tabulated in the source)
K_t per Table 5.34 (full load at tip - conservative; §5.2.3 HPSTC charts run ~20% lower when teeth share load)
What each shaft’s bearings carry
Pinion shaft
| Tangential Wt | 1,698 lb |
| Separating W′r = Wt·tanφ (Eq 11.23) | 618 lb |
| Resultant radial Wr (Eq 11.24) | 1,807 lb |
| Bearing A (4.13 in from the mesh) | 903 lb |
| Bearing B (4.13 in) | 903 lb |
Gear shaft
| Tangential Wt | 1,698 lb |
| Separating W′r = Wt·tanφ (Eq 11.23) | 618 lb |
| Resultant radial Wr (Eq 11.24) | 1,807 lb |
| Bearing A (4.33 in from the mesh) | 903 lb |
| Bearing B (4.33 in) | 903 lb |
Spur gears generate no calculable axial thrust but tend to "walk" - restrain or allow small axial movement (§11.4.1). Driving-member bearing loads act opposite its rotation; driven-member loads act with its rotation (§11.2.3).
Enter the spacing in your chosen units, or leave it blank for a safe default: a straddle spread of at
least 70% of the pitch diameter, or an overhang spread of at least twice the overhang. Straddle bearings push back against the mesh
load; the far bearing on an overhung shaft is dragged the same way the load points.
- Sizing: Q-factor Eqs 4.53–4.58, Table 4.14 (part-05d)
- Allowables: Table 4.16 (large industrial spur, 335/300 HB)
- K_a: Table 5.37 (part-07c); applied as design K = index ÷ K_a (API 613 rule, part-09)
- Teeth: Table 3.7; pitch: Table 3.12; depth: Table 3.13
- Addendum split: Table 3.2 (balanced strength); backlash: Table 3.4
- Checks: contact ratio Eq 3.2; scoring Eq 4.50 vs Table 4.11
- Stress layer: s_t = K_t·U_L·K_d (Eq 5.90, K_t Table 5.34 tip-loaded), s_c = C_k·√(K·C_d) (Eq 5.95, C_k Eq 5.114 C_p=2300, I at pinion LPSTC per Fig 5.36); K_m Table 5.38, K_v AGMA velocity curves, K_s/C_s §5.2.6; allowables - index-derived from the Table 4.16 practice (allowable-stress charts Figs 5.24–5.27 are not tabulated in the source)
- Bearing reactions: W′_r = W_t·tanφ (Eq 11.23), W_r vector sum (11.24); straddle Fig 11.11 / overhung Fig 11.10 lever rules (part-12a/12b)
Every table and equation above points to Dudley’s Handbook of Practical Gear Design and
Manufacture. The oil and gas material rows come from API 613.
One job, sized for every industry
This is your exact job worked out to the standard of every industry at once. Toward the demanding end the set gets smaller and lighter, paid for with harder steel, tighter tolerances and better finishing. The automotive point also leans on a short, hard life rather than the long life the others assume. The highlighted point is the design you have now.
How the sizing works
- The overall size. Your power, speed and ratio set how big the set has to be. The sheet grows the center distance until the surface load carried by the teeth sits right at the limit your industry allows, no bigger than it needs to be.
- The tooth count. The pinion starts with as many teeth as its hardness and ratio allow, then drops teeth until the bending load on a tooth also fits under the limit. Pitch snaps to a standard size, and the two counts are chosen so every tooth eventually meets every other (a hunting mesh). If the teeth still cannot carry the load, the whole set grows and tries again.
- The proportions. Tooth height, depth and backlash follow standard practice for the ratio and finish you chose. The finished pair is then checked for smooth overlap between teeth, a safe rim speed for its accuracy, and freedom from scoring at your oil and temperature.
Before you cut metal
- This is a starting point, not a final rating. The numbers here get you a set that will almost certainly pass a full AGMA or ISO rating. Run that rating, with the dynamic, mounting and reliability factors your project calls for, before you commit.
- The industries are trade-offs, not a ranking. An aerospace set is not “better” than an industrial one. It is simply harder, finer and inspected more closely, at a price to match. Choose the one your shop can actually build and afford.
- The tooth details are ready to cut. Counts, pitch, tooth height, depth and thickness are laid out the way a shop drawing expects. To draw the full tooth form for either member, with pin measurements and STEP, DXF or STL files, carry it to the Involute Gear Design sheet.
Sources
- Radzevich, S. P., Dudley’s Handbook of Practical Gear Design and Manufacture. The sizing, tooth counts, proportions and strength limits on this sheet all come from this book.
- API Standard 613. Special-purpose gear units for oil, gas and chemical service, and the basis for the oil and gas option.
- AGMA. The 2001, aerospace and vehicle rating practices behind the aerospace and automotive options.
- Wikipedia: Gear train. A plain-language primer on ratio, hunting teeth and center distance.
Disclaimer
Recommendations on application design and material selection are based on available technical data and are offered as suggestions only. Each user should make their own tests to determine the suitability for their own particular use. Standards Applied LLC offers no express or implied warranties concerning the form, fit, or function of a product in any application.
Third-party trademarks are the property of their respective owners and are used on this website for informational purposes only. No affiliation with, and no sponsorship or endorsement by, such third-party trademark owners is claimed or implied.