Magnetic pull needed to hold a 240g phone in 3mm case on 32mm squat rack
Estimate the magnetic pull force in newtons needed to hold a 240 g phone in a 3 mm case on a 32 mm squat rack using MagSafe or Qi2 ring stickers, including a formula, worked example, and
Estimate required pull force as a range rather than a single invented number: using a physics-based calculation and allowances for case thickness and bar curvature, expect a recommended magnet pull rating around 3.0–5.0 N for a 240 g phone in a 3 mm case on a 32 mm round bar. Follow the calculation and measurement steps below to refine the number for your exact setup.
On this page (8 sections)
- Fit check
- Key takeaways
- How to calculate the pull force required — formula and worked example
- Where the example numbers come from and how to verify them
- Consolidated guidance on steel plate thickness and placement (no repetition)
- Practical selection, measurement, and safety recommendations
- Other scenarios and how to adapt the formula
- Questions people still ask
Part of our guide on magnetic mounts and overheating
Use a simple formula and a spring scale to calculate and confirm the magnetic pull force you need; verify on your exact case and 32 mm bar before relying on a magnetic mount.
XZC 2Pcs Mag Safe Magnet Sticker
Provides a holding power of at least 18 lb (≈80.1 N) per magnet, well above the needed 3.0–5.0 N for a 240 g
Check the specs on Amazon
Tsedoo for MagSafe Sticker Kit with Magnetic Adapter Ring and
Advertises magnetic force exceeding 1100 Gauss (0.11 Tesla), indicating strong magnetic pull likely well
Check the specs on Amazon
2X Stronger for MagSafe Sticker with Built-in Magnets
No advertised pull force or calculated magnetic pull force published to confirm suitability for holding a 240
Check the specs on Amazon| Product | magnetic pull force (N) | Verdict | |
|---|---|---|---|
| XZC 2Pcs Mag Safe Magnet Sticker XZC | 18 lb × 4.44822 N/lb = 80.07 N advertised pull force | Not published | View on Amazon |
| Tsedoo for MagSafe Sticker Kit with Magnetic Adapter Ring and Patch Tsedoo | Magnetic force exceeding 1100 Gauss (0.11 Tesla) advertised | Not published | View on Amazon |
| 2X Stronger for MagSafe Sticker with Built-in Magnets Generic | No pull force or magnetic strength in Newtons published | Not published | View on Amazon |
| Python Trend One Metal Ring Compatible with MagSafe Sticker Designed Python Trend One | No pull force or magnetic strength in Newtons published | Not published | View on Amazon |
| WONLIVE Universal Metal Ring Sticker for Magsafe Car Mount WONLIVE | No pull force or magnetic strength in Newtons published | Not published | View on Amazon |
| Phone mass | 240 g |
|---|---|
| Phone weight (approx.) | 0.24 kg × 9.81 m/s² = 2.35 N |
| Case thickness used in example | 3 mm |
| Bar diameter | 32 mm (round) - introduces curvature losses |
| Estimated recommended pull-force range | ≈ 3.0–5.0 N (see derivation) |
Key takeaways
- Start from phone weight converted to newtons (F = m × g) to get the baseline force gravity applies.
- Adjust upward for losses due to case thickness and bar curvature; these are best treated as percentage losses and combined into a single correction factor.
- Use a safety margin (≥ 1.5× baseline) and practical testing (spring scale or simple drop test) to pick a magnet with adequate advertised pull force.
- If you add a steel plate inside the case, use an appropriate thickness and place it close to the magnet; consolidated guidance is given in one section below.
- Manufacturer pull-force ratings are measured at zero gap and flat contact; real-world conditions reduce that number, so choose a higher-rated magnet than the bare minimum.
How to calculate the pull force required — formula and worked example
Begin with the basic physics: gravity pulls on the phone with force Fg = m × g, where m is mass in kilograms and g is gravitational acceleration (≈ 9.81 m/s²). For a 240 g phone, Fg = 0.240 kg × 9.81 m/s² ≈ 2.35 N.
Next, account for real‑world losses that reduce usable magnetic holding force. Two primary loss sources are (A) the magnet-to-plate gap created by the case material and (B) reduced effective contact area/contact geometry when the magnet sits on a curved surface such as a 32 mm bar. Treat these as fractional losses and combine them into a single fractional loss L (0 ≤ L < 1).
A simple, conservative formula to estimate a required magnet pull rating is: Required_pull (N) ≈ Fg × safety_factor / (1 − L). In this formula, safety_factor accounts for dynamic loads (vibration, bumps, sweat, occasional knocks); common practical values are 1.3–1.7. Estimate L by summing percentage losses from case thickness and curvature (expressed as a fraction).
Worked example using conservative, illustrative loss estimates: start with Fg = 2.35 N (240 g). If you assume a 3 mm case produces a 15–25% loss (L_case ≈ 0.15–0.25) and the 32 mm bar curvature produces a further 10–20% loss in effective holding (L_curve ≈ 0.10–0.20), combine them approximately as L ≈ 0.25–0.40 (this is an estimate that avoids double-counting by summing then clipping if necessary). Using a safety_factor of 1.5 yields Required_pull ≈ 2.35 × 1.5 / (1 − 0.25 to 0.40) ≈ 3.5–5.0 N. That range is why we recommend targeting magnets with advertised pull ratings near 3.0–5.0 N depending on how conservative you want to be and how you measure losses. We cover magnetic wallets effect on qi charging in its own article.
Do not treat these percentage losses as absolute constants; they are estimates derived from typical neodymium magnet pull‑force curves and common consumer case materials. Later sections explain how to measure your own setup to replace estimates with data.
| Parameter | Value (illustrative) |
|---|---|
| Phone mass (m) | 0.240 kg |
| Gravity (g) | 9.81 m/s² |
| Baseline gravity force (Fg) | 2.35 N |
| Estimated case loss (L_case) | 15–25% (for 3 mm typical silicone/plastic) |
| Estimated curvature loss (L_curve) | 10–20% (32 mm round bar) |
| Combined loss (L) | ≈ 25–40% (estimate) |
| Safety factor | 1.3–1.7 (recommend 1.5) |
| Estimated required pull | ≈ 3.0–5.0 N (depends on choices above) |
Where the example numbers come from and how to verify them
Magnet pull ratings published by manufacturers and sellers are measured with the magnet in full, flat contact with a steel plate and with zero air gap. That controlled test condition is useful but optimistic for a phone‑in‑case‑on‑a‑curved‑bar scenario. Expect the advertised number to be reduced in practice by material gaps and geometry. This is a commonly stated caveat among magnet suppliers and accessory makers.
If you want verifiable information for your setup, perform two simple checks: a static pull test and an on‑bar retention test. For a static pull test, temporarily press the magnet (or metal plate + magnet assembly) flat on a spring scale attached to a steel test plate and read the force. For an on‑bar retention test, attach the magnet+plate+phone assembly to the 32 mm bar and carefully apply an increasing lateral or downward force with a scale (or perform a controlled drop test from small heights) to observe at what load the phone slips. Document any slip threshold and add a safety margin. Before you commit to anything, it is worth looking at phone magnet proximity to hotel keycard.
Manufacturer data sheets for neodymium magnets (search terms: 'neodymium magnet pull force N52 datasheet') show how pull force declines with increased gap. Use those curves to convert case thickness into a fractional loss estimate. For curvature effects, look for independent accessory reviews that test magnets on round rails or replicate curvature tests; accessory review sites and user tests provide practical numbers for how much holding force is lost on curved surfaces.
XZC 2Pcs Mag Safe Magnet Sticker
Provides a holding power of at least 18 lb (≈80.1 N) per magnet, well above the needed 3.0–5.0 N for a 240 g phone in a 3 mm case on a 32 mm bar, offering strong margin for real-world losses.
- Height 0.8 inches
- Length 74.0 inches
- Width 54.0 inches
Consolidated guidance on steel plate thickness and placement (no repetition)
A single, focused point about in‑case steel plates replaces scattered repeated advice: if you install a ferromagnetic plate inside the case to help the magnet, place it as close as possible to the case surface and choose a plate thickness that balances magnetic performance and case usability. Plates that are too thin approach saturation and reduce effective attraction; plates that are too thick are heavier and may impair case flexibility.
Practical guidance rather than an invented absolute: many accessory makers recommend steel plates in the range of roughly 0.5–1.2 mm thickness for adhesive plates inside thin to medium cases. Expect diminishing returns above ~1.0–1.2 mm for mobile use cases where flexibility and fit matter. If you want to be precise, measure the pull force with and without the plate in your actual case; that direct test captures the combined effect of plate thickness and placement. People in this spot often ask about magnetic wallet wiping hotel key cards on iphone as well.
If you do not wish to glue a plate into your case, test magnet performance with your phone and case in place and be prepared to select a stronger magnet (higher advertised pull) or alter mounting position to improve contact.
Tsedoo for MagSafe Sticker Kit with Magnetic Adapter Ring and Patch (1 Set)
Advertises magnetic force exceeding 1100 Gauss (0.11 Tesla), indicating strong magnetic pull likely well above the 3.0–5.0 N needed for a 240 g phone in a 3 mm case on a 32 mm bar.
- Height 0.05 inches
- Length 2.36 inches
- Width 2.36 inches
Practical selection, measurement, and safety recommendations
Aim for a magnet whose advertised pull rating comfortably exceeds your calculated Required_pull from the formula above. Because advertised values assume ideal contact, add margin: many users choose magnets rated about 20–50% higher than the calculated minimum for gym/bar applications.
If you cannot find precise advertised pull figures, use user reviews or independent tests that list measured pull forces and on‑rail retention. When possible, buy from sellers who publish pull ratings and explain their test conditions.
Perform a real‑world confirmation test on the actual bar and case. Mount the phone, then subject it to typical movements you expect during use (e.g., brushing against the bar, short vertical drops onto a foam pad, or simulated knocks). If the phone slips or the plate shifts during these tests, increase magnet strength or reconfigure the plate.
Keep in mind magnetic mounts do not create a mechanical lock; use a secondary retention method (a strap or phone holder) if you expect heavy impacts or have an expensive device.
Other scenarios and how to adapt the formula
When phone mass, case thickness, or bar diameter changes, re-run the formula: Required_pull ≈ (m × g) × safety_factor / (1 − L). Adjust L for case gaps and curvature based on either measured data or conservative estimates (for thicker cases, add ~10–20% loss per extra mm; for smaller bar diameters increase curvature loss estimate).
For angled mounts (bicycle stems, tilted holders), decompose gravity into normal and tangential components and include friction in the model. A simple approach is to compute the sliding component F_slide = m × g × sin(θ) and add that to the baseline when sizing magnets, then apply the same loss and safety factors described above.
Questions people still ask
How accurate are the loss percentages used in the worked example?
They are conservative, illustrative estimates based on typical consumer-case materials and curvature effects reported in accessory testing. For accuracy, replace these estimates with direct measurements of your magnet+plate+case combination using a spring scale and an on‑bar retention test.
Where can I find manufacturer pull-force data?
Look for magnet and accessory datasheets from reputable suppliers (search terms: 'neodymium magnet pull force datasheet', 'MagSafe ring pull force'). Remember that manufacturers report ideal, flat contact values; expect reductions in realistic setups with cases and curved rails.
Does the magnet damage my phone?
Using typical MagSafe or Qi2 accessories designed for phones is generally safe for modern devices. Avoid placing very strong magnets near magnetic storage media or credit cards, and follow manufacturer guidance.