The fit comparison
Compare the published fit limits
The capacity figures come from different sources. Ask for the exact user limit and usable seat measurements where the listing is incomplete.
Scroll across the table for every fit check.
| Model | Published load | Seat width | Fit check |
|---|---|---|---|
| Steelcase Series 1, Onyx A lower seat with a depth slider | 150 kg, Steelcase UK | 44 cm published | Check seat width and arm spacing independently. |
| FlexiSpot ErgoX Pro Essential, grey Higher listed load capacity | 250 kg, selected listing | Confirm usable seat width | Ask for arm gap and normal-use limit. |
Find the rating for the assembled chair
Use the maker’s maximum user weight for the exact model and revision. A rating for a cylinder, wheel set or test load on its own does not establish the user limit of the assembled chair. Ask whether the rating applies during normal seating and use of the tilt mechanism, and whether the maker specifies a particular base or set of castors.
Keep the written reply or specification with the product code. When a listing and manual give different figures, ask the manufacturer to confirm the intended limit. If you cannot resolve it, compare a chair with a clear user rating. Check any replacement parts against the same configuration.
Steelcase Series 1 has a 150 kg UK figure
Steelcase UK lists 150 kg as the supported user weight for Series 1. Its UK specifications also give a 44 cm seat width and an inside arm range of 43–51 cm. Use the weight figure for the exact chair and check whether both widths suit you in your normal setting.
A lower seat with a depth slider
Steelcase Series 1, Onyx
The UK Series 1 specifications list a 41 cm starting seat height and a usable depth range of 42–48 cm. A slider lets you trial the shorter setting.
Steelcase uses a standardised measuring method. Try the seat with your own footwear if you are near the minimum, and check armrest and castor fit at your desk.
- 41–52 cm seat height
- 42–48 cm usable depth
- Depth slider
For example, a 46 cm inside arm gap might allow you to sit between the arms, while the seat underneath may still be too narrow. Use the seat-width guide to measure the part of the pan that supports you.
FlexiSpot ErgoX Pro Essential has a higher listed capacity
The selected grey ErgoX Pro Essential listing gives 250 kg and includes a seat-depth slider and multi-position arms. The listing’s overall width describes the chair envelope. Ask FlexiSpot for the usable pan width, inside arm gap and the maximum user weight for the exact grey variant in normal use and recline.
Higher listed load capacity
FlexiSpot ErgoX Pro Essential, grey
The grey Essential listing states a 250 kg load capacity, with an adjustable seat slider and multi-position armrests.
Confirm the user limit for normal seated use and recline, plus the usable seat width and arm gap. The listed overall width includes the chair’s outer parts.
- 250 kg Amazon UK listing figure
- Seat-depth adjustment
- Multi-position arms
Check the arms at the width you will use and look for room at the front corners of the seat. A broad-looking chair may still have raised edges or narrow brackets. If you need a replacement wheel or arm part later, confirm that it is approved for the chair and intended loading.
Check supported movement as well as dimensions
Sit with feet supported, then move to the normal working position and try the manufacturer’s tilt and lock controls. Check whether the chair stays at its selected height and whether you can get in and out without catching the arms or base. Leave room between the desk and your legs at that seat height.
Record the confirmed user limit, the pan width, the arm gap and the seat range. If the seller cannot confirm a dimension you need, ask for a measured photograph or try the exact chair before committing.
Common questions
Does a weight rating tell me how wide the chair is?
Check the seat pan and arm gap separately. The rating describes the load supported under the maker’s conditions.
Can I use the gas-lift rating as the chair limit?
Use the rating for the complete chair. The lift is only one of the parts carrying the load.
Does fitting heavier-duty wheels raise the chair’s weight rating?
Use the complete chair’s confirmed rating and maker-approved wheels. The wheel rating alone cannot change that figure.
Is an advertised test load the same as user capacity?
Check how the maker defines it. Ask for the maximum user weight in normal use for the exact model.
What should I do if two figures disagree?
Ask the maker to confirm the user limit for the exact configuration and intended use before buying.
Sources and selection
Sources and Amazon UK listings checked in November 2026. Fit examples use published specifications. The selected Amazon UK listings supply the specifications for FlexiSpot ErgoX Pro Essential, grey.