How to Use This Calculator

Getting your spindle spacing right is crucial for safety and aesthetics. Here’s how to get the most accurate results:

Measuring Your Railing Distance

The inside railing distance is the actual space where your spindles will be installed. Measure between the inner faces of your posts or walls. If you’re installing a new end post, subtract its width from your total measurement. For example, if your total length is 2500mm and you’re adding a 100mm post, your inside distance is 2400mm.

Choosing Your Spindle Width

For plain square spindles, measure the actual width. For turned spindles with decorative profiles, always measure at the thinnest point. This matters because building regulations check spacing using a 100mm sphere, and it must not pass through at any point. Metal spindles are typically thinner, usually around 12-16mm.

Which Spacing Method Should You Pick?

Centred spindles give you balanced gaps at each end, creating a symmetrical appearance. This works brilliantly when your railing sits between two equal posts. Evenly-spaced throughout means every gap is identical, including the end spaces. This looks cleaner when your railing meets different structures at each end. Not certain? Select “both options” and see which appeals to you more.

Staircase Measurements

When calculating for stairs, you can enter the riser height and tread run to determine slanted spacing. This becomes important if your spindles have varying widths or you’re using fillet strips between them. The calculator automatically adjusts for the stair angle to give you diagonal measurements.

Quick Reference Guide

Common Spindle Sizes in the UK

Standard Railing Lengths

Typical domestic staircases in the UK have railing lengths between 2000mm and 4000mm per flight. Landing balustrades vary widely but commonly range from 1000mm to 3000mm. Always measure your specific installation rather than assuming standard sizes.

Building Regulations Explained

UK building regulations (Approved Document K) specify that “a 100mm sphere cannot pass through any openings in the guarding.” This applies to both stairs and landings.

Why 99mm Maximum?

The 99mm spacing limit exists to prevent small children from getting their heads stuck between spindles. Building inspectors often carry a 100mm ball to test compliance. If the ball fits through, your installation fails inspection and needs rectifying before you can complete your project.

Measuring for Turned Spindles

Turned spindles present a specific challenge. Their decorative profiles create thinner sections, which is where the 100mm sphere test applies. You must measure spacing from the narrowest points, not the widest sections. This typically means you’ll need one or two additional spindles compared to plain square spindles.

Horizontal vs Vertical

Regulations primarily focus on vertical spindles. Horizontal spindles can create a climbing hazard, particularly concerning for children. Many local authorities require specific approval for horizontal designs, and some prohibit them entirely. Check with your local building control before considering horizontal spindles.

Step-by-Step Installation

Before You Start

Order 5-10% more spindles than calculated to account for damage during cutting or installation. Check each spindle for defects before installation. Ensure your base rail and handrail grooves match your spindle width.

Marking Out

1. Use the calculator to determine your exact spacing measurements
2. Mark the position of your first spindle from the starting post
3. Mark remaining positions using your calculated spacing
4. Double-check measurements before cutting or drilling
5. Use a straight edge to verify alignment

Cutting Spindles

Measure each position individually for stairs, as heights may vary slightly. Cut spindles square using a mitre saw for clean edges. For slanted base rails, cut the bottom of each spindle at the appropriate angle to sit flush.

Securing in Place

Most systems use either grooved rails or individual fixings. For grooved systems, slide spindles into the base rail groove, position correctly, then secure with panel pins or adhesive. Add the handrail groove over the tops and secure. For direct-fix systems, drill pilot holes to prevent splitting, then screw each spindle into the tread and handrail.

Common Questions Answered

Troubleshooting Common Mistakes

Too Few Spindles Ordered

This happens when people measure the outer railing length instead of the inside distance, or forget to account for turned spindle profiles. Always measure between the inner faces of posts. If you’ve already ordered, check if your spacing still meets the 99mm maximum before installation.

Uneven End Gaps

When people divide the total length by the number of spindles without accounting for end spacing, they get uneven results. The calculator handles this by offering centred versus even spacing options. Choose the method that suits your installation.

Forgetting About Angles

Stair spindles sit at an angle. If you measure along the handrail rather than horizontally, your spacing will be too wide when viewed straight on. The calculator’s slanted spacing feature accounts for this automatically when you enter riser and tread measurements.

Wrong Measurement Points

For turned spindles, measuring at the widest point gives false confidence. The sphere test applies to the narrowest section. Always use the minimum width in your calculations, even if it means slightly closer spacing than aesthetically preferred.

Material Considerations

Wooden Spindles

Pine offers affordability and easy workability, perfect for painted finishes. Oak provides superior durability and attractive grain for natural finishes. Hemlock sits between the two in price and durability. All wood species expand and contract with humidity changes, so account for seasonal movement in your installation method.

Metal Spindles

Metal spindles allow for slimmer profiles due to material strength. This means fewer spindles per metre compared to wood, reducing material costs despite higher per-unit prices. Powder-coated finishes last decades without maintenance. Wrought iron designs add period character but require professional fabrication.

Mixing Materials

Contemporary designs often combine wooden newel posts and handrails with metal spindles. This pairing reduces visual bulk whilst maintaining strength. Calculate metal spindle spacing separately from any wooden sections, as their different widths require different quantities.

Finish Compatibility

Pre-finished spindles save installation time but limit customisation. Raw spindles need sanding and finishing, adding labour but allowing perfect colour matching. If painting, primer before installation prevents bare wood showing in grooves after seasonal movement.

Cost Planning

Budgeting for Materials

Spindle costs vary dramatically by material and design. Budget pine spindles start around £2-3 each, whilst decorative turned oak spindles can reach £15-20 each. Metal spindles typically cost £5-12 per unit. For a typical domestic staircase needing 50-60 spindles total, material costs range from £100 to £1,200.

Hidden Costs

Don’t forget base rails, handrails, newel posts, and fixings. These often equal or exceed spindle costs. Professional installation typically charges £500-1,500 depending on complexity and location. DIY installation requires proper tools: mitre saw, drill, level, and safety equipment.

When to Hire Professionals

Straight landing balustrades suit confident DIY installers. Complex staircases with turns, winders, or cut strings benefit from professional installation. Building regulations compliance falls on the installer, so mistakes become expensive to rectify. Get multiple quotes and check insurance coverage before proceeding.

Special Situations

Open-Tread Stairs

When spindles mount directly to treads rather than a continuous base rail, calculate spacing along the tread length. Each tread becomes a separate calculation section. Ensure spindles fix securely into the tread edge, typically requiring 40-50mm depth for proper support.

Curved Staircases

Curved sections need spindles radiating from the curve’s centre point. This creates varying gaps at inner versus outer edges. Measure spacing along the outer edge (longest path) to comply with regulations. Specialist curved handrails and base rails require professional fabrication.

Diminishing Staircases

Where ceilings slope down to meet the staircase, spindles gradually decrease in height. Calculate spacing as normal along the railing length, then measure individual heights for each spindle position. This requires careful measurement and cutting for each piece.

Quarter Landings

The corner section of a quarter landing needs either a newel post or mitred handrails with continuous spindles. For continuous spindles around corners, calculate the straight sections separately, then space corner spindles to match adjacent straight sections visually.

References

The following sources provide authoritative guidance on UK staircase regulations and spindle installation:

• HM Government (2013). The Building Regulations 2010: Approved Document K – Protection from falling, collision and impact (2013 edition incorporating 2013 amendments). NBS, London.
• British Standards Institution (2018). BS 5395-1:2010+A1:2018 – Stairs. Code of practice for the design of stairs with straight flights and winders. BSI Standards Limited, London.
• British Standards Institution (2017). BS 6180:2011+A1:2017 – Barriers in and about buildings. Code of practice. BSI Standards Limited, London.
• National House Building Council (2022). NHBC Standards 2022 – Chapter 8.1: Internal walls, partitions and ceilings. NHBC, Milton Keynes.