How to Measure for Silicone Breast Forms: A Step-by-Step Guide
Getting measured correctly takes about four minutes. Getting it wrong costs the price of a breast form. This guide gives you the exact steps — what to measure, how to measure it, what the numbers mean, and what to do when the numbers don't match a standard size chart.
Read this before you buy. The size decision guide covers what to do with your measurements once you have them — this guide covers how to get accurate measurements in the first place.
What You Need Before You Start
One soft measuring tape — the kind used for sewing and body measurements, not a rigid metal tape measure. If you don't have one, a piece of string and a ruler work as a substitute: wrap the string, mark the measurement point, then measure the string against the ruler.
A mirror — full-length if possible, or at minimum a mirror that shows the chest area. You need to be able to see the tape position while measuring.
A pen and paper, or a notes app. You'll take three measurements and you need to record all three accurately. Don't rely on memory.
Wear a bra or no top at all — not a padded bra, not a sports bra with significant compression, not a heavily structured garment. The measurements need to reflect the actual chest, not the chest as shaped by a garment.
Step 1: Understand What You're Measuring and Why
Three measurements drive the breast form size decision. Each one answers a different question.
Chest circumference answers: what bra band size do I need? This measurement determines the bra that will hold the breast forms, which in turn determines how the breast forms sit and how the silhouette reads.
Chest width answers: what is the maximum base width of breast form that will sit naturally on my chest? This is the single most important measurement for avoiding the most common sizing mistake — choosing a breast form whose base is wider than the chest, which pushes the breast forms into the armpit area.
Desired cup size is not a measurement of the body — it's a decision about the silhouette. It's included here because it needs to be decided in the context of the first two measurements, not independently of them.
Step 2: Taking the Three Measurements
Measurement 1: Chest circumference.
Stand upright with arms relaxed at your sides. Place the tape measure around the ribcage, directly under where the breast forms will sit — the same position as a bra band. The tape should be parallel to the floor all the way around. It should be snug against the skin but not tight — you should be able to slide two fingers under the tape. Breathe normally and take the measurement at the end of a normal exhale. Record the number in centimetres or inches, whichever you'll use for the size chart.
⚠️ Common error: measuring too high (across the fullest part of the chest rather than under it) or too low (across the stomach). The correct position is directly under where the breast forms will sit — typically 2–3cm below the nipple line on a natural chest.
Measurement 2: Chest width.
Stand in front of the mirror with arms relaxed at your sides. Place your hands flat on your chest, fingers pointing toward each other. Identify the natural boundary of the chest on each side — the point where the chest meets the armpit. This is the outer boundary of where the breast forms can sit without extending into the armpit area. Measure the distance between these two boundary points across the chest. This is your maximum base width.
⚠️ Common error: measuring the full width of the torso rather than the chest boundary. The chest boundary is where the chest meets the armpit — not the widest point of the torso. If you're unsure, err on the side of a narrower measurement. A breast form that's slightly narrower than the maximum base width is better than one that's slightly wider.
Measurement 3: Desired projection reference.
This is not a tape measure measurement — it's a visual reference. Stand in front of the mirror and look at your chest in profile. Note the current projection of the chest — how far it extends forward from the ribcage. The breast forms will add projection on top of this baseline. A wearer with significant existing chest tissue will need less projection from the breast forms to achieve a given silhouette than a wearer with a flat chest. Note whether your baseline projection is: flat (minimal existing tissue), moderate (some existing tissue), or significant (substantial existing tissue). This note will inform the projection decision in the size chart.
Step 3: Converting Measurements to Size Chart Numbers
Breast form size charts vary between manufacturers — Femmevee's size chart uses the chest circumference and desired cup size as the primary inputs, with the chest width as a constraint check.
Using the chest circumference. Find your chest circumference measurement on the size chart. This gives you the band size range — the range of breast form sizes that will work with a bra in your band size. All breast form sizes within this band size range are physically compatible with your chest circumference.
Applying the chest width constraint. From the sizes within your band size range, eliminate any whose base width exceeds your chest width measurement. The base width of each breast form size is listed in the product specifications. This step eliminates the sizes that would extend beyond the natural chest boundary — regardless of how appealing they look in the size chart.
Selecting within the remaining range. From the sizes that remain after the chest width constraint is applied, select based on the desired cup size and projection. If you're between sizes, choose the smaller one for the first purchase. For the full decision framework, see our size decision guide.
Step 4: Recording Your Numbers
Record all three measurements in a format you can refer back to — not just for this purchase, but for future purchases as the body changes.
A simple record format:
| Measurement | Your Number | Date Measured | Notes |
|---|---|---|---|
| Chest circumference | Band size: ___ | ||
| Chest width (max base width) | Maximum base width: ___cm | ||
| Baseline projection | Flat / Moderate / Significant | ||
| Size selected | Cup: ___ Weight: ___g |
Dating the measurements matters. The body changes — with age, with weight change, with HRT, with surgery — and measurements taken today may not be accurate in 12 months. A dated record allows you to track changes and know when remeasurement is needed.
When to Remeasure
Remeasure whenever there's a reason to think the measurements have changed. Specific triggers:
Weight change of more than 5kg. Weight change affects chest circumference and, to a lesser extent, chest width. A 5kg weight change is a reasonable threshold for remeasurement — smaller changes are unlikely to affect the size decision significantly.
Starting or changing HRT. Hormone replacement therapy changes the chest — both the tissue and the shape — in ways that affect both measurements. Remeasure at 6-month intervals during active HRT, or whenever the current breast forms feel noticeably different in fit. For more on sizing during transition, see our HRT guide.
After mastectomy or chest surgery. Surgery changes the chest anatomy in ways that require fresh measurements. Post-surgical measurements should be taken after the surgical swelling has fully resolved — typically 6–8 weeks post-surgery, or as directed by the surgical team. For post-mastectomy sizing guidance, see our post-mastectomy guide.
After age 50. The chest changes with age — skin elasticity decreases, tissue redistributes, and the chest shape changes in ways that affect how breast forms sit. Remeasure every 1–2 years after 50, or whenever the current breast forms feel different in fit. For age-specific guidance, see our mature wearers guide.
When the current breast forms feel wrong. If the breast forms that fitted correctly when purchased now feel too large, too small, or sit differently than they used to — remeasure before assuming the breast forms are the problem. The body may have changed; the measurements will confirm whether a new size is needed.
Measuring for Specific Body Types
Plus-size bodies. For plus-size wearers, the chest width measurement is particularly important — the chest boundary may be wider than standard size charts assume, which means a wider range of base widths is available. Don't assume that a larger chest circumference requires a proportionally larger breast form — the chest width measurement is the constraint, not the circumference. For detailed guidance on plus-size sizing, see our body proportion guide.
Asymmetric chests. Minor chest asymmetry — which is extremely common — doesn't require different measurements for each side. Take the measurements as described and select a size based on the average. The breast forms will create a symmetrical silhouette regardless of minor underlying asymmetry. Significant asymmetry — such as post-mastectomy asymmetry — may require different sizes for each side; the post-mastectomy guide covers this in detail.
Athletic builds. Athletic builds — with developed pectoral muscles — may have a chest width that's wider than the circumference measurement suggests. Take the chest width measurement carefully, as the pectoral muscle boundary may extend further toward the armpit than on a less muscular build. The chest width constraint is particularly important for athletic builds to avoid breast forms that extend into the armpit area.
From Measurements to Purchase
Once you have accurate measurements, the purchase decision involves two more steps: selecting the size within the range the measurements define, and selecting the bra that will hold that size correctly. The size decision guide covers the first step in detail. For the bra selection step — which is inseparable from the size decision — see our bra guide.
For first-time buyers who want the complete purchase picture — beyond measurements and size — see our buying guide.
Multiple Sizes · Detailed Size Chart · Platinum Silicone · Discreet Shipping
Femmevee Silicone Breast Forms
Femmevee's detailed size chart lists base width, projection, and weight for every size — the numbers you need to apply the measurements in this guide. Take your measurements, apply the chart, and arrive at a size decision grounded in your actual body rather than guesswork.
From $89.00
View Size Chart →Quick Questions
Q: My chest circumference falls between two band sizes — which do I use?
A: Round down to the smaller band size. Bra bands stretch with wearing; a band that's snug when new will loosen slightly over time. A band that's too loose from the start will not provide adequate support for the breast forms.
Q: I measured my chest width but I'm not sure I identified the boundary correctly — how do I check?
A: Put on a well-fitted bra and look in the mirror. The outer edge of the bra cup — where the cup meets the side band — marks approximately where the chest boundary is. The breast form base width should not exceed the width of the bra cup from centre to outer edge, multiplied by two.
Q: My measurements suggest a size that looks smaller than I want — should I go up?
A: The measurements define the range of sizes that will sit naturally on your chest. Going above the range — choosing a breast form whose base width exceeds your chest width — will create a silhouette that looks unnatural regardless of how appealing the larger size looks in the size chart. Work within the range the measurements define; the projection decision within that range gives you significant control over the silhouette.
Q: How often should I remeasure?
A: Whenever there's a reason to think the measurements have changed — weight change of more than 5kg, HRT changes, surgery, or when the current breast forms feel different in fit. Otherwise, every 1–2 years is a reasonable interval for routine remeasurement.
Q: The breast forms I ordered don't fit the way the measurements suggested — what went wrong?
A: Check the bra fit first — a correctly sized breast form in a poorly fitted bra will not sit correctly. If the bra fits correctly and the breast forms still don't sit right, see our troubleshooting guide for specific fit problems and their solutions.
Further Reading
- Size Decision Guide — what to do with your measurements once you have them
- Buying Guide — the complete first purchase decision
- Body Proportion Guide — size selection for specific body types
- Bra Guide — selecting the right bra for your size
- HRT Guide — remeasuring during hormonal transition
- Post-Mastectomy Guide — measuring after chest surgery
- Mature Wearers Guide — remeasuring as the body changes with age
- Troubleshooting Guide — when the size doesn't fit as expected