Elevator pit depth and overhead calculator

Minimum pit depth and overhead for a traction elevator from rated speed, buffer type, runbys and car heights, by ASME A17.1/CSA B44 or EN 81-20.

Still needs a trade check. Treat each point below as unconfirmed, not as code, until it is checked against a licensed copy of the cited edition:

ASME governor: the upper tripping speed limit in Table 2.18.2.1 is unconfirmed for every spring-buffer estimate. No table is stored here. Verify the governor setting against the adopted edition; accepting an input does not confirm its code limit.
ASME: the 600 mm (24 in) pit clearance and refuge, the 600 mm (24 in) clearance above car top equipment, the 1100 mm car top clearance, the jump basis and the buffer rules were confirmed in the public text of A17.1-2016; the 2019 edition cited here still needs a trade check.
EN 81-20: the 500 mm clearance above car roof equipment was read from the public draft (prEN 81-20), not the published standard. The 1000 mm pit and car roof refuge heights, the 1.0 m/s spring buffer limit, the spring stroke of at least 0.135 v² and 65 mm, and the subclause numbers still need a trade check.
Runbys, car height and equipment heights are planning allowances, not code values.

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Result

Minimum pit depth: 52.4 in (4 ft 4.4 in)
Minimum overhead: 162.0 in (13 ft 6.0 in)
Buffer stroke: 2.8 in
Jump allowance: 1.4 in
Space below the car on its buffer: 43.7 in (3 ft 7.7 in)
Space above the car roof: 47.7 in (3 ft 11.7 in)

Not engineering advice; a licensed professional checks every result. Not a substitute for a licensed engineer, the manufacturer's data or the authority having jurisdiction; confirm the code edition your jurisdiction has adopted. First build: the code limits used here await a trade check against a licensed copy of the cited edition. Terms of use and estimate disclaimer.

Drawing

How the pit depth and the overhead add up.

Working

Oil buffer stroke (115% of rated speed, at most 1 g)
$S = \dfrac{(1.15v)^2}{2g_n}$
S = (1.15 × 1.016)² ÷ (2 × 9.80665) ≈ 69.604 mm
= 70 mm (rounded up)
Space below the car when it rests on its compressed buffer
$B = \max(e_b + c_p,\; h_{rp})$
B = max(500 + 609.6, 609.6) = 1109.6 mm
= 1110 mm
Minimum pit depth
$P = R_c + S + B$
P = 150 + 69.6037158458801 + 1109.6 ≈ 1329.204 mm
= 1330 mm (rounded up)
Jump allowance (half the gravity stopping distance at 115%)
$J = \tfrac{1}{2}\,\dfrac{(1.15v)^2}{2g_n}$
J = 0.5 × (1.15 × 1.016)² ÷ (2 × 9.80665) ≈ 34.802 mm
= 35 mm (rounded up)
Space above the car roof
$T = \max(e_t + c_t,\; h_{rt})$
T = max(600 + 609.6, 1100) = 1209.6 mm
= 1210 mm
Minimum overhead (top landing floor to hoistway ceiling)
$O = H_c + R_w + S + T + J$
O = 2600 + 200 + 69.6037158458801 + 1209.6 + 34.80185792294 ≈ 4114.006 mm
= 4115 mm (rounded up)

Working is shown in the units each formula is written in; the result figures above follow the unit switch. A numeric input is taken to 15 significant digits before it is used (1033.2293579541322 kg is used as 1033.22935795413 kg); every echo of it shows that value, and a computed figure substituted into the working is quoted to 15 significant digits as well.

Notes

The pit allows 609.6 mm below the lowest car part and a 609.6 mm refuge (ASME A17.1/CSA B44-2019, 2.4.1); the overhead allows 609.6 mm above roof equipment and a 1100 mm car top refuge (ASME A17.1/CSA B44-2016, 2.4.6 and 2.4.7).
Working in US units: A17.1 prints the pit clearance, the pit refuge and the clearance above car top equipment as 24 in, which is 609.6 mm, more than the 600 mm SI figure, so the US figure is used. The car top clearance stays 1100 mm, more than the 43 in A17.1 prints.
Minimum dimensions are rounded up, never to nearest: the working shows the exact sums to 0.001 mm, and every figure quoted as a minimum is at or above them.
This covers traction elevators, with the counterweight buffer stroke taken equal to the car buffer stroke. Hydraulic elevators follow other rules and come in a later release.
Runbys, car height and equipment heights are planning allowances: replace them with the manufacturer's figures for the equipment chosen.

Method

Pit depth

With the car level at the bottom landing, it sits a runby above its buffer. If it overruns, it travels that runby, then compresses the buffer through its full stroke. Below the platform there must still be room for the equipment hung under the car plus a clear space to the pit floor, and enough height for a person to shelter in the pit refuge. The pit depth is the sum of the runby, the buffer stroke and the larger of those two space needs.

For oil buffers the stroke is computed: the buffer must be able to stop a car arriving at 115 percent of rated speed with an average retardation no greater than gravity, so the stroke is the gravity stopping distance from 1.15 v. For spring buffers you enter the maker's stroke; EN 81-20 asks for at least 0.135 v squared and 65 mm, and both codes keep spring buffers to speeds of 1.0 m/s or less. ASME A17.1 prints that limit as 1.0 m/s (200 ft/min); the two figures are not exact equivalents, so the speed is checked against the figure printed in the unit system you work in.

Overhead

With the car level at the top landing, the counterweight sits a runby above its own buffer. If the car overruns upward, the counterweight lands and compresses its buffer, and the car can keep rising by a further jump as the ropes go slack. Above the car roof there must be room for the equipment on the roof plus a clearance, or for the car top refuge, whichever is taller.

The overhead is the car height plus the counterweight runby, the buffer stroke, that space above the roof, and the jump. ASME A17.1 bases the jump on half the gravity stopping distance at 115 percent of rated speed with oil buffers, and at the governor tripping speed with spring buffers. EN 81-20 states it as 0.035 v squared metres, which is almost the same number.

Limits of this calculator

It is a planning estimate for traction elevators. The runbys, car height and equipment sizes are allowances you should replace with the chosen manufacturer's figures, and the counterweight buffer is assumed to have the same stroke as the car buffer. Reduced-stroke buffers with emergency terminal speed limiting, and hydraulic elevators, are not covered.

Formulas

Oil buffer stroke

S = (1.15 v)^2 / (2 g_n), g_n = 9.80665 m/s²

S = \dfrac{(1.15v)^2}{2g_n}

Pit depth

P = car runby + S + max(equipment below + pit clearance, pit refuge height)

P = R_c + S + \max(e_b + c_p,\; h_{rp})

Jump (ASME, oil buffers)

J = 0.5 (1.15 v)^2 / (2 g_n)

J = \tfrac{1}{2}\,\dfrac{(1.15v)^2}{2g_n}

Jump (ASME, spring buffers)

J = 0.5 v_t^2 / (2 g_n), v_t = governor tripping speed (m/s), g_n = 9.80665 m/s²

J = \tfrac{1}{2}\,\dfrac{v_t^2}{2g_n}

Jump (EN 81-20)

J = 0.035 v^2 (m)

J = 0.035v^2

Overhead

O = car height + counterweight runby + S + max(equipment above + top clearance, top refuge height) + J

O = H_c + R_w + S + \max(e_t + c_t,\; h_{rt}) + J

Code basis: clause and edition

Standard	Edition	Clause	What it covers
ASME A17.1/CSA B44	2019	2.4.1	Bottom car clearance and pit refuge
ASME A17.1/CSA B44	2016	2.4.6 and 2.4.7	Checked public source for the jump and top clearances; the adopted 2019 edition remains unverified
ASME A17.1/CSA B44	2016	2.18.2.1	Governor tripping speed minimum; the table maximum is unconfirmed
ASME A17.1/CSA B44	2019	2.22.1.1, 2.22.3 and 2.22.4	Spring buffer speed limit, and spring and oil buffer strokes
EN 81-20	2020	5.2.5.7 and 5.2.5.8	Headroom and pit clearances and refuge spaces
EN 81-20	2020	5.8.2	Buffer strokes

Rules are restated in our own words and computed for your inputs; no table or text from a standard is reproduced. The adopted edition varies by jurisdiction, so confirm the one your authority having jurisdiction enforces.

Inputs

Input	Unit	Range	Default
Code `standard`	choice	asme, en	asme
Rated speed `ratedSpeed`	metres per second (m/s)	0.1 to 4	1.016
Buffer type `bufferType`	choice	oil, spring	oil
Spring buffer stroke `springStroke`	millimetres (mm)	30 to 400	100
Governor tripping speed `tripSpeed`	metres per second (m/s)	0.1 to 4	1.1684
Car runby `carRunby`	millimetres (mm)	50 to 600	150
Counterweight runby `cwtRunby`	millimetres (mm)	50 to 900	200
Car height `carHeight`	millimetres (mm)	2000 to 4500	2600
Equipment above the car roof `equipAbove`	millimetres (mm)	0 to 1500	600
Equipment below the platform `equipBelow`	millimetres (mm)	0 to 1500	500
System the code limits are checked in `units`	choice	si, us	si

Worked examples

Each example below is a test the calculator must pass before it ships. The expected values were worked out by a separate implementation.

Example	Expected result (each in its declared unit)
ASME, 1.0 m/s, oil buffers, default allowances	bufferStroke: 67.5 mm, pitDepth: 1317.5 mm, overhead: 4101.2 mm, jump: 33.8 mm
EN 81-20, 1.6 m/s, oil buffers	bufferStroke: 172.7 mm, pitDepth: 1322.7 mm, overhead: 4162.3 mm, jump: 89.6 mm
EN 81-20, 0.63 m/s, spring buffers of 80 mm	bufferStroke: 80 mm, pitDepth: 1230 mm, overhead: 3993.9 mm, jump: 13.9 mm
ASME, 1.0 m/s, spring buffers of 100 mm, governor tripping at 1.4 m/s	bufferStroke: 100 mm, pitDepth: 1350 mm, overhead: 4150 mm, jump: 50 mm

For AI agents

This calculator is also the MCP tool elevator_pit_overhead at https://elevatorcalc.com/api/mcp, using the same function as this page. See how to connect, the llms.txt file, or the JSON catalogue.